40 litres of milk cost ₹48 a litre. How much water must be added so that the mixture costs ₹40 a litre?

Explanation

1. 01

   Water : milk $= (48 - 40) : (40 - 0) = 8 : 40 = 1 : 5$.

2. 02

   For 40 litres of milk, $\frac{40}{5} = 8$ litres of water. Check: $\frac{1{,}920}{48} = 40$.