Two sums of ₹40000 each are invested on the same day — one at 20% per annum compounded annually for 2 years, the other at 10% per annum compounded annually for 4 years. The difference between the two maturity amounts (in ₹) is:

First: $40000\times 1.$$20^2$ = ₹57600. Second: $40000\times 1.$$10^4=40000\times 1.4641$ = ₹58564. Difference ₹964, in favour of the longer, gentler investment. (Under SIMPLE interest both would earn 40% of ₹40000 = ₹16000 and the answer would be ₹0 — that is the trap, because halving a rate and doubling the time keeps SI unchanged but not CI, which rewards the extra compoundings. ₹1600 and ₹2564 are how far each investment beats plain simple interest, not the gap between them.)