A dishonest delivery man purchases 20 litres of pure milk and dilutes it by adding 4 litres of water. If he sells the diluted milk at Rs. 50/L, then what is the cost price of pure milk ?

Rs. 60/L

$\text{Milk purchased}=20\text{ L}.$

$\text{Water added}=4\text{ L}.$

$\text{Total mixture}=24\text{ L}.$

$\text{Selling price}=₹50\text{ per L}.$

$\text{Total selling price}=24\times50=₹1200.$

$\text{Cost price of milk per L}= \frac{1200}{20}.$

$=₹60.$

$\text{Cost price of pure milk}=₹60\text{ per litre}.$