The quantity of water that must be added to 36 litres of pure milk at \(1\displaystyle\frac{1}{2}\) litres for Rs. 75 so as to have mixture worth Rs. 40 a litre is :
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → 9 litres
Cost price of pure milk:
\( \displaystyle \frac{75}{1.5} = 50 \) rupees per litre
Water costs nothing, so the total cost stays the same after mixing:
\(36 \times 50 = 1800\) rupees
Let w litres of water be added. The mixture of (36 + w) litres is to be worth Rs. 40 a litre:
\(40(36 + w) = 1800\)
\(36 + w = 45\)
\(w = 9\)
So 9 litres of water must be added.