A trader mixes 6ltr of milk costing 500 TK. with 7ltr of milk costing 600 TK. per litre. The trader also mixes some quantity of water to the mixture so as to bring the price to 480 TK. per litre. How many litres of water is added?

Question: A trader mixes 6ltr of milk costing 500 TK. with 7ltr of milk costing 600 TK. per litre. The trader also mixes some quantity of water to the mixture so as to bring the price to 480 TK. per litre. How many litres of water is added?

Solution:
Let us consider, the water be 'W' litre

Here,
(6 × 500 + 7 × 600)/(13 + W) = 480
⇒ 3000 + 4200 = 6240 + 480W
⇒ 480W = 7200 - 6240
⇒ W = 960/480
∴ W = 2

W is the amount of water added, W = 2 litre