Successive discounts of $10 \%$,$20 \%$ and $50 \%$ will be equivalent to a single discount of .......... $\%$

$A$ shopkeeper cheats to the extent of $10 \%$ while buying as well as selling by using false weights. His total gain percentage is:

$A$ trader marked the selling price of an article at $10 \%$ above the cost price. At the time of selling,he allows a certain discount and suffers a loss of $1 \%$. He allowed a discount of $\%$:

By selling $90$ pens for $Rs. 80$,a man loses $20\%$. What should be the selling price (in $Rs.$) of $90$ pens for $20\%$ profit?

The cost price of an article is $64 \%$ of the marked price. The gain percentage after allowing a discount of $12 \%$ on the marked price is........$\%$

On a $Rs. 10,000$ payment order,a person has a choice between three successive discounts of $10\%, 10\%$ and $30\%$ and three successive discounts of $40\%, 5\%$ and $5\%$. By choosing the better offer,how much can he save in $Rs.$?