$A$ trader purchases 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 total profit of $Rs. 51.50$. The difference between the original prices of the pendulum and the watch is equal to? (in $Rs.$)

An electric pump was sold at a profit of $15 \%$. Had it been sold for $Rs. 600$, the profit would have been $20 \%$. What was the former selling price in $Rs.$?

$A$ person sells two articles,each for $Rs. 1040$. He incurs $20 \%$ loss on the first and $10 \%$ loss on the second. Find out the overall percent loss.

Instead of dividing $391$ cookies among $3$ children $A, B, C$ in the ratio $\frac{1}{5}: \frac{1}{4}: \frac{1}{8}$,they were divided in the ratio $5: 4: 8$. Who gains the most and how many?

$A$ 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 $Rs.$)

$A$ shopkeeper gains $17 \%$ after allowing a discount of $10 \%$ on the marked price of an article. Find his profit percent if the article is sold at the marked price allowing no discount. (in $\%$)