If the ratio of the cost price and selling price of an article is $20: 21$,then what will be the profit percent (in $\%$)?

$A$ man purchased some eggs at $3$ for $Rs. 5$ and sold them at $5$ for $Rs. 12$. Thus,he gained $Rs. 143$ in all. The number of eggs he bought is:

Two discounts of $40 \%$ and $20 \%$ are equal to a single discount of what percentage?

The list price of an article at a showroom is $Rs. 2000$ and it is being sold at successive discounts of $20 \%$ and $10 \%$. Its net selling price will be (in $Rs.$)

Harkesh bought a certain quantity of tomato at the rate of $Rs. 1500$ per quintal. $10 \%$ of the tomato was spoiled. At what price in $Rs.$ per quintal should he sell the remaining to gain $20 \%$ of his outlay?

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