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Worked Examples · Example 1

Q.In an economy, the marginal propensity to consume (MPC) is 0.75. If autonomous investment increases by ₹800 crore, calculate

(i) the investment multiplier, and
(ii) the resulting change in national income. Also state how much of this increase in income is consumption-induced.
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✓ Free question

Step 1 — Compute the multiplier.

The investment multiplier is k=11−MPCk = \dfrac{1}{1-MPC}. Here MPC=0.75MPC = 0.75, so:

k=11−0.75=10.25=4k = \dfrac{1}{1-0.75} = \dfrac{1}{0.25} = 4

Step 2 — Compute the change in income.

ΔY=k×ΔI=4×800=₹3,200 crore\Delta Y = k \times \Delta I = 4 \times 800 = ₹3{,}200 \text{ crore}

Step 3 — Split the increase into the initial injection and the consumption-induced part.

Of the total ₹3,200 crore rise in income, ₹800 crore is the original autonomous investment itself; the remaining

₹3,200−₹800=₹2,400 crore₹3{,}200 - ₹800 = ₹2{,}400 \text{ crore}

is the additional income generated purely through successive rounds of induced consumption spending (each round re-spending 75% of the previous round's extra income: 600 + 450 + 337.5 + … , a geometric series summing to 2,400).

Independent check (geometric-series method). The multiplier process is ΔI(1+MPC+MPC2+MPC3+… )=ΔI1−MPC\Delta I(1 + MPC + MPC^2 + MPC^3 + \dots) = \dfrac{\Delta I}{1-MPC}, which for ΔI=800\Delta I = 800 and MPC=0.75MPC = 0.75 again gives 8000.25=3,200\dfrac{800}{0.25} = 3{,}200 — confirming the formula answer independently.

✓Final answer

Investment multiplier k=4k = 4. Change in national income ΔY=₹3,200\Delta Y = ₹3{,}200 crore, of which ₹2,400 crore is consumption-induced income.

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