Quantity of fruit juice in the mixture = 70 - [70 x (10/100) ]= 63 litres. After adding water, juice would form 87.5% of the mixture. Hence, if quantity of mixture after adding x liters of water, [(87.5) /100 ]*x = 63 => x = 72 Hence 72 - 70 = 2 litres of water must be added.