$10 \%$ discount and then $20 \%$ discount in succession is equivalent to total discount of.......$\%$

A shopkeeper purchased $70$ $kg$ of potatoes for $Rs.\, 420$ and sold the whole lot at the rate of $Rs.\, 6.5$ per $kg.$ What will be his gain percent?

The market price of an article is $Rs.$ $100 .$ If the article is sold at a discount of $10 \%,$ then $35 \%$ profit is realised. How much loss or profit will be made if it is sold for $Rs.\, 30$ less than market price?

A person incurs $5 \%$ loss by selling a watch for $Rs.\,1140 .$ At what price should the watch be sold to earn $5 \%$ profit in $Rs.$?

The profit earned by selling an article for $Rs.\, 900$ is double the loss incurred when the same article is sold for $Rs.$ $450 .$ At what price should the article be sold to make $25 \%$ profit in $Rs.$?

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