$A$ person sells $36$ apples per rupee and suffers a loss of $4 \%$. Find how many apples per rupee should be sold to have a gain of $8 \%$.

$P$ invests $Rs. 9100$ for $3$ months. $Q$ invests $Rs. 6825$ for $2$ months and $R$ invests $Rs. 8190$ for $5$ months in a business. If the total profit amounts to $Rs. 4158$,how much profit should $Q$ get? (in $Rs.$)

$A$ cloth dealer professes to sell cotton at cost price, but uses a meter scale having a length of $80 \, cm$ only and charges for a full meter. Find his gain percent.

$A$ dairyman pays $Rs. 6.40$ per litre of milk. He adds water and sells the mixture at $Rs. 8$ per litre,thereby making $37.5\%$ profit. The proportion of water to milk received by the customers is

$A$ shopkeeper buys a toy at $Rs. 100$ and sells it at $Rs. 125$. Another shopkeeper buys the same toy at $Rs. 125$ but sells it at $Rs. 100$. What are the respective profit and loss percentages for the two shopkeepers?

Peter purchased a machine for $Rs. 80000$ and spent $Rs. 5000$ on repairs and $Rs. 1000$ on transport,then sold it with a $25\%$ profit. At what price did he sell the machine? (in $Rs$)