A trader purchase a wrist watch and a pendulum for $Rs.$ $390.$ He sells them making a profit of $10 \%$ on the watch and $15 \%$ on the pendulum. He earns a profit of $Rs$. $51.50 .$ The difference between the original prices of the pendulum and the watch is equal to? (in $Rs.$)

Find $CP$ when $SP = Rs.\,40 .60, \operatorname{gain}=16 \% ?$

A shopkeeper purchases two items for $Rs.\, 520 .$ One of them is sold gaining $16 \%$ and the other at a loss of $10 \%,$ thus making no profit or loss. What is the selling price of the item sold at loss?

A discount of $15 \%$ on one article is the same as a discount of $20 \%$ on another article. The costs of the two articles can be (in $Rs.$)

A tradesman gives $4 \%$ discount on the marked price and gives $1$ book free for buying every $15$ books and thus gains $35 \% .$ The marked price is increased above the cost price by (appx.) (in $\%$)

A men gains $20 \%$ by selling an article for a certain price. If he sells it at double the price, what will be the percentage of profit?