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

Maninder bought two horses at $Rs. 40,000$ each. He sold one horse at $15\%$ gain, but had to sell the second horse at a loss. If he had suffered a loss of $Rs. 3,600$ on the whole transaction, then the selling price of the second horse is (in $Rs.$)

$A$ man sells an article at a loss of $5 \%$. If he had bought it at $20 \%$ more and sold it for $Rs. 115$ less,he would have made a loss of $40 \%$. Find the cost price of the article.

$A$ trader purchases a wrist watch and a pendulum for $Rs. 390$. He sells them making a profit of $10 \%$ on the watch and $15 \%$ on the pendulum. He earns a total profit of $Rs. 51.50$. The difference between the original prices of the pendulum and the watch is equal to? (in $Rs.$)

If a stall sells a pizza at $Rs. 200$,he makes a $20 \%$ loss. If he wants to make a $10 \%$ profit,then at what price (in $Rs.$) should he sell it?

$APD$ printed $3000$ copies of 'Career Power' at a cost of $Rs. 240000$. It gave $500$ copies free to different philanthropic institutions. It allowed a discount of $25\%$ on the published price and gave one copy free for every $25$ copies bought at a time. It was able to sell all the copies in this manner. If the published price is $Rs. 325$,then what is its overall gain or loss percentage in the whole transaction?