$20 \%$ loss on selling price is what per cent loss on the cost price? (in $\%$)

$A$ shopkeeper allows a discount of $10 \%$ on the marked price of a camera. The marked price of the camera,which costs him $₹ 600$,to make a profit of $20 \%$ should be (in $₹$):

$A$ dishonest dealer professes to sell his goods at cost price but uses a weight of $960 \, g$ instead of a $1 \, kg$ weight. Find his gain $\%$. (in $\%$)

Amit buys $5$ watches for $Rs. 9450$ and later sells them for $Rs. 9700$. How much profit does Amit make per watch in $Rs.$?

By selling an article at $\frac{3}{4}$ of the marked price,there is a gain of $25 \%$. The ratio of the marked price to the cost price is:

$A$ man buys $300$ dozen of bananas for $Rs. 3,600$. He sold $1/3$ of the stock at a loss of $10\%$ and the remaining $2/3$ of the stock at a gain of $10\%$. Find his overall percent profit or loss.