The marked price of a piano was $Rs.\, 15,000$. At the time of sale, there were successive discounts of $20 \%$ $10 \%$ and $10 \%$ on it. The sale price was (in $Rs.$)

Arun purchased $30\, kg$ of wheat at the rate of $Rs.\,11.50$ per $kg$ and $20\, kg$ of wheat at the rate of $Rs.\,14.25$ per $kg$. He mixed the two and sold the mixture. Approximately at what price per $kg$ should he sell the mixture to make $30 \%$ profit? (in $Rs.$)

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

A trader sells his table at a profit of $15 \%$ and the chair at a loss of $7 \frac{1}{2} \%,$ but on the whole he gains $Rs.\, 50 .$ If he sells the table at a loss of $7 \frac{1}{2} \%,$ and chair at a profit of $15 \%,$ then he neither gains nor loses. Find the cost price of the table

The cost price of an article is $80 \%$ of its marked price for sale. How much percent does the tradesman gain after allowing a discount of $12 \% ?$