A shopkeeper gains the cost of $8$ metres thread by selling $40$ metres thread. Find his gain percent.

A man buys $10$ oranges for a rupee and sells $8$ oranges for a rupee. What is the profit percent?

A trader mixes $26\, kg$ of rice at $Rs.\, 20$ per $kg$ with $30\, kg$ of rice of another variety at $Rs.\, 36$ per $kg$ and sells the mixture at $Rs$ $30$ per $kg.$ His profit percent is

The cost price of an article is $64 \%$ of the marked price. The gain percentage after allowing a discount of $12 \%$ on the marked price is........$\%$

A shopkeeper sells one transistor for $Rs.\, 840$ at a gain of $20 \%$ and another for $Rs.\, 960$ at a loss of $4 \% .$ His total gain or loss percent is

A man purchased $150$ pens at the rate of $Rs.\, 12$ per pen. He sold 50 pens at gain of $10 \% .$ The percentage gain at which he must sell the remaining pens so as to gain $15 \%$ on the whole outlay is........$\%$