NCERT Solutions for Class 12 Economics Chapter 4: Determination of Income and Employment

These Class 12 Economics Chapter 4 solutions cover Determination of Income and Employment from the NCERT textbook Introductory Macroeconomics, updated for the 2026–27 session. The chapter builds the Keynesian model of income determination under a fixed price level and a constant rate of interest. You will learn the consumption function, the meaning of ex ante and ex post values, how equilibrium income is fixed where aggregate demand equals aggregate supply, the working of the investment (autonomous expenditure) multiplier, the paradox of thrift and the idea of full-employment income. Below are step-by-step solutions to all six NCERT exercise questions — with every multiplier and equilibrium-income numerical worked out and verified — plus key formulas, extra practice, MCQs, Assertion–Reason questions and FAQs.

Class: 12 Subject: Economics Book: Introductory Macroeconomics Chapter: 4 Title: Determination of Income and Employment Session: 2026–27
On this page

Class 12 Economics Chapter 4 – Overview

Chapter 4, Determination of Income and Employment, develops the simple Keynesian model of national-income determination. To isolate the forces that fix income, it assumes a fixed price of final goods and a constant rate of interest (the ceteris paribus assumption), so that aggregate supply is perfectly elastic and output is decided solely by aggregate demand. Aggregate demand is made up of planned (ex ante) consumption and planned investment: consumption follows the function C = C̄ + cY, where C̄ is autonomous consumption and c is the marginal propensity to consume; investment is taken as autonomous (I = Ī). Equilibrium income is reached where ex ante aggregate demand equals ex ante aggregate supply (the 45° line), giving Y = (C̄ + Ī)∕(1 − c). A change in autonomous spending changes income by a magnified amount through the investment multiplier 1∕(1 − c). The chapter closes with the paradox of thrift — the result that a rise in the desire to save can leave total saving unchanged — and with full-employment income, showing that equilibrium need not mean full employment of resources (deficient or excess demand may exist).

Key Concepts & Terms

Ex ante vs ex post: ex ante (planned) values are what households and firms intend to consume, invest or produce; ex post (realised) values are what actually happened, as recorded in the accounts. Income determination uses ex ante magnitudes.

Aggregate demand (AD): the total planned expenditure on final goods at each level of income. In a two-sector economy, AD = C + I = (C̄ + Ī) + cY.

Aggregate supply (AS): the total value of final goods firms plan to produce. With prices fixed and resources unused, AS is perfectly elastic and shown by the 45° line (AS = Y).

Consumption function: C = C̄ + cY, splitting consumption into autonomous consumption C̄ (the amount consumed even when income is zero) and induced consumption cY (which rises with income).

Marginal propensity to consume (MPC, c): the change in consumption per unit change in income, c = ΔC∕ΔY. It lies between 0 and 1.

Marginal propensity to save (MPS, s): the change in saving per unit change in income, s = ΔS∕ΔY = 1 − c, so MPC + MPS = 1.

Autonomous expenditure (Ā): the part of aggregate demand independent of income, Ā = C̄ + Ī. A change in Ā shifts the AD line up or down in parallel.

Effective demand principle: when the price level is fixed and supply is perfectly elastic, the equilibrium level of output is determined solely by the level of aggregate demand.

Investment (autonomous expenditure) multiplier: the ratio of the total change in equilibrium income to the initial change in autonomous expenditure, k = ΔY∕ΔĀ = 1∕(1 − c) = 1∕s.

Parametric shift: a shift caused by a change in a parameter of the model — a change in the intercept (Ā) shifts the line in parallel, while a change in the slope (c) makes the line swing (rotate).

Paradox of thrift: if everyone tries to save a larger share of income (MPS rises), equilibrium income falls so much that total saving in the economy remains unchanged (or even declines).

Full-employment income: the level of income at which all factors of production are fully employed. Equilibrium income may be below it (deficient demand) or above it (excess demand).

Key Formulas

Consumption function: C = C̄ + cY  •  Saving function: S = Y − C = −C̄ + (1 − c)Y.

MPC and MPS: c = ΔC∕ΔY, s = ΔS∕ΔY, and c + s = 1.

Aggregate demand: AD = C̄ + Ī + cY = Ā + cY, where Ā = C̄ + Ī.

Equilibrium (two-sector): Y = AD ⇒ Y = (C̄ + Ī)∕(1 − c) = Ā∕(1 − c).

Investment multiplier: k = ΔY∕ΔĀ = 1∕(1 − c) = 1∕s.

Total change in income: ΔY = k × ΔĀ = ΔĀ∕(1 − c).

NCERT Exercises — Full Solutions

All questions below are reproduced verbatim from the NCERT textbook’s end-of-chapter Exercises. Answers are original, written in exam-ready style, with full working shown for every numerical.

1. What is marginal propensity to consume? How is it related to marginal propensity to save?

ANSWER Marginal propensity to consume (MPC) is the ratio of the change in consumption expenditure to the change in income that causes it. It measures the fraction of an additional unit of income that is spent on consumption. It is denoted by c and is written as c = ΔC∕ΔY. For example, if income rises by Rs 100 and consumption rises by Rs 80, then MPC = 80∕100 = 0.8. Its value lies between 0 and 1. Relation with MPS: Income is either consumed or saved, so any change in income is divided between a change in consumption and a change in saving: ΔY = ΔC + ΔS. Dividing throughout by ΔY gives 1 = (ΔC∕ΔY) + (ΔS∕ΔY) = MPC + MPS. Therefore MPC + MPS = 1, i.e. MPS = 1 − MPC. The two are complementary: a higher MPC means a lower MPS, and vice versa. In the example above, MPS = 1 − 0.8 = 0.2.

2. What is the difference between ex ante investment and ex post investment?

ANSWER Ex ante investment is the planned investment — the amount producers intend or plan to add to the stock of capital and inventories during a year, before the year’s events unfold. It reflects intentions and is the magnitude used in the theory of income determination. Ex post investment is the realised or actual investment — the amount that actually gets added to capital and inventories, as measured in the accounts at the end of the year. It includes any unplanned (unintended) change in inventories caused by sales differing from what was expected. Illustration: Suppose a producer plans to add goods worth Rs 100 to her stock (planned/ex ante investment = Rs 100). Due to an unforeseen rise in demand she has to sell Rs 30 worth of goods out of this stock. At the year-end her inventory rises by only Rs (100 − 30) = Rs 70, so her actual/ex post investment is Rs 70. Thus ex ante investment differs from ex post investment by the unplanned change in inventories (here −Rs 30). Ex ante and ex post investment are equal only when the goods market is in equilibrium and there is no unintended inventory change.

3. What do you understand by ‘parametric shift of a line’? How does a line shift when its (i) slope decreases, and (ii) its intercept increases?

ANSWER A straight line is described by the intercept-form equation Y = a + bX, in which a (the intercept) and b (the slope) are parameters — constants that fix the position and steepness of the line. A parametric shift is a change in the position of the whole line that occurs because the value of one of these parameters changes. (i) When the slope (b) decreases: the line becomes flatter and swings (rotates) downwards about its fixed intercept on the Y-axis. The point where the line meets the Y-axis stays the same, but for every positive value of X the line now lies lower than before. (In the income model, a fall in the MPC c swings the AD line downward.) (ii) When the intercept (a) increases: the line shifts upward in a parallel manner, keeping the same slope. Every point on the line rises by the same amount equal to the increase in the intercept. (In the income model, a rise in autonomous expenditure Ā shifts the AD line up in parallel.)

4. What is ‘effective demand’? How will you derive the autonomous expenditure multiplier when price of final goods and the rate of interest are given?

ANSWER Effective demand: When the price of final goods and the rate of interest are fixed, aggregate supply becomes perfectly elastic and the level of output (and hence employment) is determined solely by the level of aggregate demand. The particular level of aggregate demand at which the goods market is in equilibrium — where ex ante aggregate demand equals ex ante aggregate supply — is called effective demand, and the equilibrium level of income it fixes is the level of national income. Deriving the autonomous expenditure multiplier: In a two-sector economy aggregate demand is AD = C + I, with C = C̄ + cY and I = Ī. So AD = C̄ + Ī + cY = Ā + cY, where Ā = C̄ + Ī is autonomous expenditure. Equilibrium requires AD = Y (the 45° line), so: Y = Ā + cY ⇒ Y − cY = Ā ⇒ Y(1 − c) = Ā ⇒ Y = Ā∕(1 − c). Now suppose autonomous expenditure changes by ΔĀ. The new equilibrium income changes by ΔY = ΔĀ∕(1 − c). The autonomous expenditure multiplier (k) is the ratio of the total change in income to the change in autonomous expenditure: k = ΔY∕ΔĀ = 1∕(1 − c) = 1∕s. Because 0 < c < 1, the multiplier is greater than 1: an initial rise in autonomous spending raises income by a larger amount, since the extra income generated is partly re-spent round after round, summing the geometric series 1 + c + c² + … = 1∕(1 − c). The larger the MPC, the larger the multiplier.

5. Measure the level of ex-ante aggregate demand when autonomous investment and consumption expenditure (A) is Rs 50 crores, and MPS is 0.2 and level of income (Y) is Rs 4000 crores. State whether the economy is in equilibrium or not (cite reasons).

ANSWER Given: Autonomous expenditure Ā = Rs 50 crores; MPS = 0.2; income Y = Rs 4000 crores. Step 1 — find MPC: c = MPC = 1 − MPS = 1 − 0.2 = 0.8. Step 2 — compute ex ante aggregate demand: AD = Ā + cY = 50 + (0.8 × 4000) = 50 + 3200 = Rs 3250 crores. Step 3 — equilibrium check: The economy is in equilibrium only when ex ante aggregate demand equals output (aggregate supply), i.e. AD = Y. Here AD = Rs 3250 crores while Y = Rs 4000 crores, so AD ≠ Y. Conclusion: The economy is not in equilibrium. Since AD (3250) < Y (4000), planned demand falls short of output by Rs (4000 − 3250) = Rs 750 crores. This means there is excess supply; unsold goods pile up as unintended inventory accumulation, so producers will cut output. Income will keep falling until equilibrium is reached at Y* = Ā∕(1 − c) = 50∕(1 − 0.8) = 50∕0.2 = Rs 250 crores.

6. Explain ‘Paradox of Thrift’.

ANSWER The paradox of thrift states that if all the people of an economy increase the proportion of income they wish to save (i.e. the economy’s MPS rises, or its MPC falls), the total value of saving in the economy does not rise — it either remains unchanged or actually declines. It is a paradox because individually saving more seems sensible, yet collectively the attempt fails to raise aggregate saving. Why it happens: A fall in the MPC reduces aggregate consumption and hence aggregate demand. As demand falls below output, excess supply emerges and producers cut production. This lowers income, which lowers consumption further, and the process repeats through the multiplier — but now working in reverse. Equilibrium income falls by a magnified amount, ΔY = ΔĀ∕(1 − c). At the new, lower income, the higher saving rate is applied to a smaller income, so total saving need not increase. Numerical illustration (textbook example): Start with C = 40 + 0.8Y and Ī = 10, so Ā = 50 and equilibrium income Y₁* = 50∕(1 − 0.8) = Rs 250. Saving here = Y − C = 250 − (40 + 0.8 × 250) = 250 − 240 = Rs 10. Now suppose people become thriftier and the MPC falls from 0.8 to 0.5. New equilibrium income Y₂* = 50∕(1 − 0.5) = Rs 100. Saving now = 100 − (40 + 0.5 × 100) = 100 − 90 = Rs 10. Although the desire to save (MPS) rose from 0.2 to 0.5, total saving stays exactly Rs 10 — income has fallen from Rs 250 to Rs 100. This is the paradox of thrift.

Extra Practice Questions

Short Answer Type Questions

Q1. Distinguish between autonomous consumption and induced consumption.

ANSWERIn the consumption function C = C̄ + cY, autonomous consumption (C̄) is the consumption that takes place even when income is zero; it is independent of income. Induced consumption (cY) is the part of consumption that depends on and rises with income, governed by the MPC. For example, if C = 100 + 0.8Y, then 100 is autonomous consumption and 0.8Y is induced consumption.

Q2. Why is the aggregate supply curve drawn as a 45° line in the simple Keynesian model?

ANSWERBecause the price level is assumed fixed and resources are unused, firms supply whatever output is demanded at that price — aggregate supply is perfectly elastic. On a diagram with output demanded on the horizontal axis and output supplied on the vertical axis, “supply equals whatever is demanded” is the line where the two coordinates are equal, i.e. the 45° line through the origin.

Q3. The consumption function of an economy is C = 200 + 0.75Y. Find the saving function.

ANSWERSaving S = Y − C = Y − (200 + 0.75Y) = −200 + (1 − 0.75)Y = S = −200 + 0.25Y. Here −200 is the autonomous (dis)saving and MPS = 0.25.

Q4. If the marginal propensity to save is 0.25, calculate the value of the investment multiplier.

ANSWERMultiplier k = 1∕MPS = 1∕0.25 = 4. (Equivalently, MPC = 1 − 0.25 = 0.75, and k = 1∕(1 − 0.75) = 1∕0.25 = 4.) This means a Rs 1 rise in autonomous expenditure raises equilibrium income by Rs 4.

Q5. Distinguish between deficient demand and excess demand.

ANSWERDeficient demand exists when equilibrium income is below the full-employment level — aggregate demand is not enough to employ all resources, which tends to pull prices down in the long run. Excess demand exists when equilibrium income is above the full-employment level — aggregate demand exceeds full-employment output, which tends to push prices up in the long run.

Long Answer Type Questions

Q1. Explain the multiplier mechanism with the help of an example showing how an initial change in investment produces a larger change in income.

ANSWERThe multiplier shows how an initial change in autonomous expenditure leads to a larger, magnified change in equilibrium income through successive rounds of spending. When firms produce extra output, the value of that output becomes income for the factors of production (wages, interest, rent, profit). Households spend a fraction (the MPC) of this extra income on consumption, which becomes fresh demand and so fresh output and income in the next round, and so on. Take C = 40 + 0.8Y and Ī = 10, giving Ā = 50 and equilibrium income Y = 50∕(1 − 0.8) = Rs 250. Now let investment rise by ΔI = 10 (from 10 to 20). The first round adds 10 to income; the second round adds (0.8)(10) = 8; the third adds (0.8)²(10) = 6.4; and so on. Summing the geometric series, ΔY = 10 + (0.8)10 + (0.8)²10 + … = 10∕(1 − 0.8) = Rs 50. The new equilibrium income is 250 + 50 = Rs 300. Thus an initial increase of Rs 10 raised income by Rs 50 — the multiplier k = ΔY∕ΔĀ = 50∕10 = 5 = 1∕(1 − 0.8). The size of the multiplier depends on the MPC: the higher the MPC, the larger the multiplier.

Q2. Explain how equilibrium income is determined in a two-sector economy by the equality of aggregate demand and aggregate supply.

ANSWERIn a two-sector economy (households and firms only), aggregate demand is the sum of planned consumption and planned investment: AD = C + I = (C̄ + cY) + Ī = Ā + cY. Aggregate supply, with prices fixed and resources idle, is perfectly elastic and equals the output produced, shown by the 45° line where AS = Y. Equilibrium is reached at the level of income where ex ante aggregate demand equals ex ante aggregate supply, AD = Y — the point where the AD line cuts the 45° line. Setting Ā + cY = Y gives Y(1 − c) = Ā, so equilibrium income Y* = Ā∕(1 − c). If AD > Y, there is excess demand; inventories fall below the desired level, so firms raise output and income rises. If AD < Y, there is excess supply; unsold goods accumulate as unintended inventory, so firms cut output and income falls. Only at Y* are plans of buyers and sellers consistent, with no unintended inventory change, so income stops changing. Note, however, that this equilibrium need not be the full-employment level.

Q3. “Equilibrium level of income need not always be the full-employment level.” Discuss this statement and explain the situations of deficient demand and excess demand.

ANSWERFull-employment income is the level of income at which all the factors of production are fully employed. In the Keynesian model, equilibrium is fixed simply where aggregate demand equals aggregate supply (Y = AD); there is no guarantee that this level coincides with full employment. Equilibrium merely means that, left to itself, income will not change — even if unemployment persists. Hence equilibrium income may be below, equal to, or above the full-employment level. Deficient demand arises when equilibrium income is less than the full-employment level: aggregate demand is insufficient to employ all factors of production, so there is involuntary unemployment, and in the long run prices tend to fall. Excess demand arises when equilibrium income is more than the full-employment level: aggregate demand exceeds the output that can be produced at full employment, so output cannot rise further and, in the long run, the excess demand pushes the price level up (inflationary pressure). Government policy can therefore aim to raise demand to remove deficient demand, or curb demand to remove excess demand, so as to move equilibrium income towards the full-employment level.

MCQs & Assertion–Reason

1. In the consumption function C = C̄ + cY, the term C̄ represents:

(a) induced consumption    (b) autonomous consumption    (c) marginal propensity to consume    (d) total saving

2. If MPC = 0.75, the value of the investment multiplier is:

(a) 0.25    (b) 1.33    (c) 4    (d) 7.5

3. The sum of the marginal propensity to consume and the marginal propensity to save is always equal to:

(a) 0    (b) 0.5    (c) 1    (d) infinity

4. Planned (intended) investment is also known as:

(a) ex post investment    (b) ex ante investment    (c) realised investment    (d) unintended inventory

5. In the simple Keynesian model, aggregate supply is represented by:

(a) a vertical line    (b) a horizontal line    (c) the 45° line    (d) a downward-sloping line

6. A change in the intercept (autonomous expenditure) causes the AD line to:

(a) swing/rotate    (b) shift in parallel    (c) become vertical    (d) remain unchanged

7. If autonomous expenditure Ā = Rs 60 crores and MPC = 0.8, the equilibrium level of income is:

(a) Rs 75 crores    (b) Rs 120 crores    (c) Rs 300 crores    (d) Rs 480 crores

8. The level of income at which all factors of production are fully employed is called:

(a) equilibrium income    (b) full-employment income    (c) autonomous income    (d) disposable income

9. When aggregate demand falls short of full-employment output, the situation is called:

(a) excess demand    (b) deficient demand    (c) effective demand    (d) parametric shift

10. The paradox of thrift states that an increase in the desire to save by all households will:

(a) always raise total saving    (b) leave total saving unchanged or reduce it    (c) raise equilibrium income    (d) raise the price level

Answer key: 1-(b), 2-(c), 3-(c), 4-(b), 5-(c), 6-(b), 7-(c), 8-(b), 9-(b), 10-(b).
Working for Q2: k = 1∕(1 − 0.75) = 1∕0.25 = 4. For Q7: Y = 60∕(1 − 0.8) = 60∕0.2 = Rs 300 crores.

For each Assertion–Reason question, choose: (A) Both true and the Reason correctly explains the Assertion; (B) Both true but the Reason is not the correct explanation; (C) Assertion true, Reason false; (D) Assertion false, Reason true.

A-R 1. Assertion: The marginal propensity to consume lies between 0 and 1.

Reason: A change in consumption can never exceed the change in income that causes it.

A-R 2. Assertion: The investment multiplier is always greater than 1.

Reason: The multiplier equals 1∕(1 − c), and since 0 < c < 1, this value exceeds 1.

A-R 3. Assertion: At the equilibrium level of income there must be full employment of resources.

Reason: Equilibrium only means that income will not change by itself, even if unemployment exists.

A-R 4. Assertion: When the MPC falls, the AD line swings (rotates) downwards rather than shifting in parallel.

Reason: A change in the slope of a line, unlike a change in its intercept, causes it to swing about the intercept.

A-R 5. Assertion: In the paradox of thrift, a rise in the saving rate can leave total saving unchanged.

Reason: The higher saving rate is applied to a lower equilibrium income, so aggregate saving need not rise.

Answer key: 1-(A), 2-(A), 3-(D), 4-(A), 5-(A).

Exam Tips & Common Mistakes

How to score full marks in this chapter

Memorise the core relations — C = C̄ + cY, MPC + MPS = 1, Y = Ā∕(1 − c) and k = 1∕(1 − c) = 1∕s — and be ready to use them both ways (find income from the multiplier, or find the multiplier from income). For numericals, always write “Given”, show each step, and state the final answer with units (Rs crores). For equilibrium questions, explicitly compare AD with Y and explain the inventory adjustment (excess demand → output rises; excess supply → output falls). Use the textbook’s own example (C = 40 + 0.8Y, Ī = 10, Y = 250 → 300) to illustrate the multiplier and the paradox of thrift, and always distinguish ex ante (planned) from ex post (realised) magnitudes.

Common mistakes to avoid

  • Confusing MPC with APC (and MPS with APS): MPC = ΔC∕ΔY is marginal; APC = C∕Y is average.
  • Writing the multiplier as 1∕MPC — it is 1∕(1 − MPC) = 1∕MPS.
  • Mixing up ex ante (planned) and ex post (realised) investment, or forgetting the unintended inventory change.
  • Saying a change in the intercept makes the line “swing” — an intercept change shifts it in parallel; only a slope change makes it swing.
  • Assuming equilibrium income always equals full-employment income — it may show deficient or excess demand.
  • Forgetting units, or skipping the final equilibrium check (AD = Y) in numerical problems.

Frequently Asked Questions

What is Chapter 4 of Class 12 Economics (Introductory Macroeconomics) about?

Chapter 4, Determination of Income and Employment, presents the simple Keynesian model of how national income is fixed under a constant price level and rate of interest. It covers the consumption function, ex ante and ex post values, equilibrium income where aggregate demand equals aggregate supply, the investment (autonomous expenditure) multiplier, the paradox of thrift and the idea of full-employment income.

How do you calculate the investment multiplier?

The investment (autonomous expenditure) multiplier is k = ΔY∕ΔĀ = 1∕(1 − c) = 1∕MPS, where c is the marginal propensity to consume. For example, if MPC = 0.8 then MPS = 0.2 and the multiplier is 1∕0.2 = 5, so a Rs 1 rise in autonomous expenditure raises equilibrium income by Rs 5.

How many questions are there in the Class 12 Economics Chapter 4 NCERT exercise?

The end-of-chapter Exercises of Introductory Macroeconomics Chapter 4 contain 6 questions — a mix of theory (MPC and MPS, ex ante vs ex post investment, parametric shift, effective demand, paradox of thrift) and a numerical on measuring aggregate demand and checking equilibrium. All six are solved step by step on this page.

← Chapter 3: Money and Banking Introductory Macroeconomics (all chapters) Chapter 5: Government Budget and the Economy →
Scroll to Top