If a man reduces the selling price of a fan from $Rs. 400$ to $Rs. 380$,his loss increases by $2 \%$. The cost price of the fan is (in $Rs.$)

$A$ merchant buys $4000 \, kg$ of wheat,one-fifth of which he sells at a gain of $5 \%$,one-fourth at a gain of $10 \%$,one-half at a gain of $12 \%$,and the remainder at a gain of $16 \%$. If he had sold the whole at a gain of $11 \%$,he would have made $Rs. 72.80$ more. What was the cost price of the crop per $kg$? (in $Rs.$)

$A$ vendor bought toffees at $6$ for a rupee. How many for a rupee must he sell to gain $20 \%$?

When a book is sold at its Marked Price,it gives a profit of $40 \%$. What percentage of profit or loss will occur if it is sold at half the Marked Price?

$A$ shopkeeper sells notebooks at the rate of $Rs. 457$ each and earns a commission of $4\%$. He also sells pencil boxes at the rate of $Rs. 80$ each and earns a commission of $20\%$. How much total commission will he earn in two weeks if he sells $10$ notebooks and $6$ pencil boxes a day?

If cost price is $Rs. 150$ less than the selling price and profit is $20 \%$,then what is the selling price (in $Rs.$)?