Given, If a shirt bought 40% discount instead of 30%, then the customer saves Rs. 15. Formula: SP = MP × (100 – Discount%)/100 Calculation: Let MP of the shirt be Rs. 100x According to the question100x × [70/100] – 100x × [60/100] = 15 ⇒ 70x – 60x = 15 ⇒ 10x = 15 ⇒ x = 15/10 ⇒ x = 1.5 MP of the shirt = 100 × 1.5 = Rs. 150 .∴ Selling price of the shirt if it is sold 50% discount = 150 × (50/100) = Rs. 75 Smart Method 40%−30%=10%=15 Hence, 50%=15×5=75.