$A$ man has $60$ pens. He sells some of these at a profit of $12 \%$ and the rest at $8 \%$ loss. On the whole,he gets a profit of $11 \%$. How many pens were sold at $12 \%$ profit?

How many kg of sugar costing ₹ $11.70/kg$ must be mixed with $24$ $kg$ of sugar costing ₹ $8.1/kg$ so that there may be a gain of $15 \%$ by selling the mixture at ₹ $9/kg$? (in $kg$)

In what ratio must $25 \%$ hydrochloric acid be mixed with $60 \%$ hydrochloric acid to get a mixture of $40 \%$ hydrochloric acid?

Two casks of $48$ $litres$ and $42$ $litres$ are filled with mixtures of wine and water,the proportions in the two casks being respectively $13:7$ and $18:17$. If the contents of the two casks are mixed,and $20$ $litres$ of water is added to the whole,what will be the proportion of wine to water in the resultant mixture?

In a mixture of $75 \ L$,the ratio of milk to water is $2:1$. The amount of water to be further added to the mixture so as to make the ratio of the milk to water $1:2$ will be (in $L$):

In what ratio must water be added to spirit to gain $10 \%$ by selling it at the cost price?