The amount of water that must be added to 51 litres of milk at 2 litres for 120 so as to have mixture worth ₹45 litre is :

17 litres

The correct answer is Option (3) → 17 litres

Price of Pure Milk = $\frac{120}{2}=60$ per litre

Let amount of water added be x litre

Total volume = $(51+x)L$

$⇒\frac{51×60}{51+x}=45$

$5060=45(51+x)$

$⇒x=\frac{765}{45}=17$