Gold is $19$ times as heavy as water and copper is $9$ times as heavy as water. In what ratio should these metals be mixed so that the mixture may be $15$ times as heavy as water?

$100$ $litres$ of a mixture contains $20 \%$ water and the rest is milk. The amount of milk that must be added so that the resulting mixture contains $87.5 \%$ milk is (in $litres$):

Two vessels contain milk and water in the ratio $3:2$ and $7:3$. Find the ratio in which the contents of the two vessels have to be mixed to get a new mixture in which the ratio of milk and water is $2:1$.

Aditya and Sanjay started a business investing $45000$ and $30000$ respectively. What will be the ratio between their profit?

$A$ bottle full of whisky contains $50 \%$ alcohol. $A$ part of this whisky is replaced by another containing $18 \%$ alcohol and the percentage of alcohol was found to be $26 \%$. The quantity of whisky replaced is

$8$ litres are drawn from a cask full of wine and is then filled with water. This operation is performed three more times. The ratio of the quantity of wine now left in the cask to that of water is $16:65$. How much wine did the cask hold originally? (in litres)