A department store's coupon reads: '30% off on the part of your bill above ₹1000.' A shopper whose bill comes to ₹2500 uses the coupon. Reckoned on the whole bill, the discount she gets is what percent?

Only ₹1500 of the bill qualifies, so the money saved is 30% of 1500 = ₹450, and 450/2500 = 18%. (Equivalently, 60% of the bill qualifies and 30% of 60% is 18%.) Reading the coupon as 30% off everything gives 30%; applying it to the FIRST ₹1000 instead of the part above it gives ₹300, or 12%; and 60% is merely the share of the bill that the coupon touches, not the discount.