A cooperative bank cuts the interest it pays on savings accounts from 4% per annum to 3% per annum. The interest earned on a given deposit therefore falls by what percent?

On a deposit of ₹100 the interest drops from ₹4 to ₹3, a fall of ₹1 on ₹4 = 25%. (The rate falls by 1 percentage point, which is not the same as 1%; and 75% is the share of the interest that survives, not the share lost.)