A sum is invested at compound interest, the interest being credited at the end of every year. The interest credited in the second year is ₹5000, and the interest credited in the third year is ₹600 more than that. The rate of interest per annum is what percent?

Each year's interest is the previous year's interest grown by the same rate, because it is earned on an amount larger by exactly that factor. The third year's interest is ₹5600, so 5600/5000 = 1.12 and the rate is 12%. (Measuring the ₹600 rise against the third year's ₹5600 gives 10.7% — the rise has to be compared with the previous year's interest, not the later one.)