A shopkeeper sells oil. He marks up the price of oil to 50% above its cost price and offers a discount of 20% on the marked price upon selling it. If the shopkeeper cheats his customer by selling 'y' ml less in every 1 litre pack of oil, he earns a profit of Rs. 1680 on selling 6 packets of oil. If 1 litre of oil is sold honestly without cheating in quantity, then the difference between the discount given and the profit earned is Rs. 80. Find the value of (2y + 30).

Let the cost price of 1 litre of oil be Rs. 100m Marked price of 1 litre of oil = 100m X 1.5 = Rs. 150m Selling price of 1 litre of oil = 150m X 0.8 = Rs. 120m Profit without cheating = 120m - 100m = Rs. 20m Discount given = 150m - 120m = Rs. 30m ATQ, 30m - 20m = 80 Or, 10m = 80 So, m = 8 Cost price of 1 litre of oil = 100 X 8 = Rs. 800 Selling price of 1 litre of oil = 120 X 8 = Rs. 960 Selling price of (1000 - y) ml of oil = Rs. 960 Profit earned on selling 6 packets of (1000 - y) ml oil = Rs. 1680 So, profit earned on selling (1000 - y) ml oil = 1680 ÷ 6 = Rs. 280 So, cost price of (1000 - y) ml oil = 960 - 280 = Rs. 680 (680/800) = {(1000 - y) /1000} 0.85 X 1000 = 1000 - y So, 'y' = 1000 - 850 = 150 Therefore, required value = 2y + 30 = 300 + 30 = 330