Zinc and copper are in the ratio $5:3$ in $400 \, g$ of an alloy. How much copper (in $g$) should be added to make the ratio $5:4$?

$A$ trader has $50 \ kg$ of sugar,a part of which he sells at $10 \%$ profit and the rest at $5 \%$ loss. He gains $7 \%$ on the whole. What is the quantity sold at $10 \%$ gain and $5 \%$ loss? (in $kg$)

$A$ mixture contains $80 \%$ acid and the rest water. The part of the mixture that should be removed and replaced by the same amount of water to make the ratio of acid and water $4:3$ is

In three vessels,the ratio of water and milk is $6:7$,$5:9$,and $8:7$,respectively. If the mixtures of the three vessels are combined,what will be the final ratio of water to milk?

$A$ trader has $50 \text{ kg}$ of rice,a part of which he sells at $10 \%$ profit and the rest at $5 \%$ loss. He gains $7 \%$ on the whole. What is the quantity sold at $10 \%$ gain and $5 \%$ loss? (in $\text{kg}$)

$A$ mixture of $40$ $litres$ of milk and water contains $10 \%$ water. How much water must be added to make $20 \%$ water in the new mixture? (in $Liters$)