$A$ man purchased $150$ pens at the rate of $Rs. 12$ per pen. He sold $50$ pens at a gain of $10 \%$. The percentage gain at which he must sell the remaining pens so as to gain $15 \%$ on the whole outlay is........$\%$

If a discount of $10 \%$ is given on the marked price of a radio,the gain is $20 \%$. If the discount is increased to $20 \%$,the gain is......$\%$

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........$\%$

$A$ $TV$ set is being sold for $Rs. x$ in Chandigarh. $A$ dealer went to Delhi and bought the $TV$ at a $20\%$ discount (from the price of Chandigarh). He spent $Rs. 600$ on transport. Thus,he sold the set in Chandigarh for $Rs. x$,making a $14 \frac{2}{7}\%$ profit. What was $x$ in $Rs.?$

$A$ trader marked his goods at $20 \%$ above the cost price. He sold half the stock at the marked price,one quarter at a discount of $20 \%$ on the marked price,and the rest at a discount of $40 \%$ on the marked price. What is his total gain percentage?

$A$ reduction of $21\%$ in the price of an item enables a person to buy $3\, Kg$ more for $₹ 100$. The reduced price of the item per $Kg$ is (in $₹$):