$50 \, g$ of an alloy of gold and silver contains $80 \%$ gold (by weight). The quantity of gold,that is to be mixed with this alloy,so that it may contain $95 \%$ gold,is (in $g$)

$A$ 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

Tea worth ₹ $126/kg$ and ₹ $135/kg$ are mixed with a third variety in the ratio $1:1:2$. If the mixture is worth ₹ $153/kg$,the price of the third variety per kg will be (in ₹):

In a $40 \, L$ mixture of milk and water,the ratio of milk to water is $7:1$. In order to make the ratio of milk and water $3:1$,the quantity of water (in $litres$) that should be added to the mixture will be:

$A$ man buys $2$ cows for $Rs. 2700$ and sells one at a loss of $6\%$ and the other at a gain of $7.5\%$. On the whole,he neither gained nor lost. What is the cost price of the $2^{nd}$ cow?

$300$ $gm$ of sugar solution contains $40 \%$ sugar. How much sugar (in $gm$) should be added to make the concentration $50 \%$ in the solution?