$A$ discount series of $10 \%$,$20 \%$,and $40 \%$ is equal to a single discount of.......$\%$

Nitin bought some oranges at $Rs. 40$ a dozen and an equal number at $Rs. 30$ a dozen. He sold them at $Rs. 45$ a dozen and made a profit of $Rs. 480$. The total number of dozens of oranges he bought was:

Ram purchased a computer set for $Rs. 12500$ and spent $Rs. 300$ on transportation and $Rs. 800$ on installation. At what price should he sell it to earn an overall profit of $15\%$? (in $Rs.$)

$A$ shopkeeper listed the price of goods at $30 \%$ above the cost price. He sells half the stock at this price, one-fourth of the stock at a discount of $15 \%$, and the remaining at $30 \%$ discount. His overall profit is.......$\%$

$A$ sold a horse to $B$ for $Rs. 4800$ by losing $20\%$. $B$ sells it to $C$ at a price which would have given $A$ a profit of $15\%$. $B$'s gain is (in $Rs.$)

Abhishek makes a profit of $Rs. 110$ if he sells a certain number of pens at the price of $Rs. 2.5$ per pen and incurs a loss of $Rs. 55$ if he sells the same number of pens for $Rs. 1.75$ per pen. How many pens does Abhishek have?