Repeated doubling under CI — from 5 years to 20 years: ₹ 12000 deposited at compound interest doubles in 5 years. What will it become after 20 years (same rate maintained)?

Introduction / Context:
If an amount doubles in a fixed interval under compound interest, then over k such intervals it multiplies by 2^k. Recognizing the number of equal intervals between the two horizons gives the final multiplier immediately.

Given Data / Assumptions:

• Principal P0 = ₹ 12000
• It doubles in 5 years
• We need the amount after 20 years at the same rate

Concept / Approach:
20 years contains 4 blocks of 5 years. Therefore, amount after 20 years is P0 * 2^4 = P0 * 16.

Step-by-Step Solution:
A(20) = 12000 * 16 = ₹ 192000

Verification / Alternative check:
Timeline view: 0→5 yrs: 12000→24000; 10 yrs: 48000; 15 yrs: 96000; 20 yrs: 192000 (four doublings).

Why Other Options Are Wrong:
₹ 120000 and ₹ 96000 reflect incorrect counts of doublings; ₹ 124000 assumes linear growth; ₹ 240000 is not a power-of-two multiple of the principal for 20 years.

Common Pitfalls:
Using SI reasoning (adding 4 * 12000) rather than multiplying by 2^4; miscounting the number of 5-year blocks in 20 years.

Final Answer:
₹ 192000