A bank card takes 8% off a restaurant bill at the counter, and the bank afterwards credits back 5% of the amount the diner actually paid. Reckoned on the original bill, the diner's total benefit is what percent?

On a bill of ₹100 he pays ₹92 and is credited 5% of 92 = ₹4.60, so the meal costs him ₹87.40 and the benefit is 12.6%. (The cashback sits on the DISCOUNTED amount, not on the bill, so adding the rates to 13% claims 5% of ₹100 that was never offered. ₹4.60 is only the cashback part, and dividing the ₹12.60 by the ₹87.40 finally borne gives 14.42% — the base for a discount is always the bill you started with.)