An alloy is made by mixing metal $A$ costing ₹ $2000/kg$ and metal $B$ costing ₹ $400/kg$ in the ratio $A:B = 3:1$. What is the cost (in ₹) of $8$ kilograms of this alloy?

The average weekly salary per head of all employees (supervisors and labourers) is ₹ $100$. The average weekly salary per head of all the supervisors is ₹ $600$,while the average weekly salary per head of all the labourers is ₹ $75$. Find out the number of supervisors in the factory if there are $840$ labourers in it.

$A$ milk vendor has $2$ cans of milk. The first contains $25\%$ water and the rest milk. The second contains $50\%$ water. How much milk should he mix from each of the containers so as to get $12$ litres of milk such that the ratio of water to milk is $3:5$?

Mira's expenditure and savings are in the ratio $3: 2$. Her income increases by $10 \%$. Her expenditure also increases by $12 \%$. By how many $\%$ does her saving increase?

$A$ shopkeeper bought $15 \text{ kg}$ of rice at the rate of $Rs. 29$ per $\text{kg}$ and $25 \text{ kg}$ of rice at the rate of $Rs. 20$ per $\text{kg}$. He sold the mixture of both types of rice at the rate of $Rs. 27$ per $\text{kg}$. His profit in this transaction is (in $Rs.$)

$A$ dishonest trader professes to sell his article at cost price but he uses $900 \, g$ weight instead of $1 \, kg$. What is the percentage gain of the trader in this trade?