The price of a school bag went up by ₹120, which was a rise of 20%. Months later the price came down by ₹120, back to what it had been. That fall of ₹120 was a fall of what per cent?

The ₹120 rise was 20%, so the old price was 120/0.20 = ₹600 and the raised price was ₹720. The same ₹120 coming off is measured on ₹720: 120/720 = 0.1667 = 16.67%. 20% is the symmetry trap - equal rupees do not mean equal per cents, because the fall works on the bigger figure. 14.29% divides by ₹840, adding the rise a second time, and 25% divides by ₹480, subtracting it instead.