$A$ 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?

In what ratio must water be mixed with milk to gain $16 \frac{2}{3} \%$ on selling the mixture at cost price?

How many $kg$ of sugar costing ₹ $5.50$ per $kg$ must be mixed with $60 \ kg$ of sugar costing ₹ $4.80$ per $kg$ so that the mixture is worth ₹ $5.25$ per $kg$?

$18 \text{ litre}$ of pure water was added to a vessel containing $80 \text{ litre}$ of pure milk. $49 \text{ litre}$ of the resultant mixture was then sold,and some more quantity of pure milk and pure water was added to the vessel in the respective ratio of $2:1$. If the resultant respective ratio of milk and water in the vessel was $4:1$,what was the quantity of pure milk added in the vessel? (in $\text{litre}$)

$60\, kg$ of an alloy $A$ is mixed with $100\, kg$ of alloy $B.$ If alloy $A$ has lead and tin in the ratio $3:2$ and alloy $B$ has tin and copper in the ratio $1:4,$ the amount of tin in the new alloy is (in $kg$)

Three containers whose volumes are in the ratio of $2:3:4$ are full of a mixture of spirit and water. In the $1^{st}$ container,the ratio of spirit to water is $4:1$,in the $2^{nd}$ container the ratio is $11:4$,and in the $3^{rd}$ container the ratio is $7:3$. All three mixtures are mixed in a big container. The ratio of spirit and water in the resultant mixture is: