$I$ have $100$ books of English. $I$ sold some of these at a profit of $12 \%$ and the rest at $8 \%$ loss. On the whole,$I$ got a profit of $11 \%$. How many books were sold at $12 \%$ profit by me?

There are $3$ tubs which contain mixtures of milk and water in the ratios of $5:2, 4:3,$ and $3:1$ respectively. If the mixtures are poured into a single tub,find the ratio of milk to water.

$A$ mixture of $30 \ L$ contains milk and water in the ratio of $7:3$. How much water should be added to it so that the ratio of milk and water becomes $3:7$? (in $L$)

In a $120$ $litre$ mixture of milk and water,water is only $25 \%$. The milkman sold $20$ $litre$ of this mixture and then added $16.2$ $litre$ of pure milk and $3.8$ $litre$ of pure water to the remaining mixture. What is the percentage of water in the final mixture (in $\%$)?

In what ratio should sugar at ₹ $30$ per $kg$ be mixed with sugar at ₹ $45$ per $kg$ so that on selling the mixture at ₹ $42$ per $kg$ there is a profit of $20 \%$?

In a mixture of milk and water with a total volume of $60$ $L$,the ratio of milk to water is $7:5$. How much water must be added to make the ratio of milk to water equal $(1:1)$? (in $L$)