$A$ dairyman pays $Rs. 6.40$ per litre of milk. He adds water and sells the mixture at $Rs. 8$ per litre,thereby making $37.5\%$ profit. The proportion of water to milk received by the customers is

$A$ trader mixes three varieties of groundnuts costing $Rs. 50$,$Rs. 20$,and $Rs. 30$ per $kg$ in the ratio $2:4:3$ by weight and sells the mixture at $Rs. 33$ per $kg$. What is the percentage of profit he makes?

If an item is sold for $Rs. 924$,there is a profit of $10\%$. What is the cost price?

$A$ cloth dealer professes to sell cotton at cost price, but uses a meter scale having a length of $80 \, cm$ only and charges for a full meter. Find his gain percent.

$A$ dealer buys an article listed at $Rs. 100$ and gets successive discounts of $10\%$ and $20\%$. He spends $10\%$ of the cost price on transportation. At what price should he sell the article to earn a profit of $15\%$? (in $Rs.$)

$A$ sells an article to $B$ at a gain of $25 \%$,$B$ sells it to $C$ at a gain of $20 \%$,and $C$ sells it to $D$ at a gain of $10 \%$. If $D$ pays $₹ 330$ for it,how much did it cost $A$? (in $₹$)