If $5 \%$ more is gained by selling an article for $Rs. 350$ than by selling it for $Rs. 340$,the cost price of the article is:

$A$ person sells a colour $TV$ at $10\%$ below the cost price. Had he received $Rs. 1494$ more,he would have made a profit of $12 \frac{1}{2}\%$. What was the cost price of the colour $TV$ (in $Rs.$)?

$A$ shopkeeper sold a $TV$ set for $Rs. 17940$ with a discount of $8 \%$ and earned a profit of $19.6 \%$. What would have been the percentage of profit earned if no discount was offered (in $\%$)?

$A$ sells an article to $B$ at a gain of $20 \%$,$B$ sells it to $C$ at a gain of $10 \%$,and $C$ sells it to $D$ at a gain of $12 \frac{1}{2} \%$. If $D$ pays $Rs. 29.70$,what was the cost price for $A$? (in $Rs.$)

If the selling price is doubled,the profit triples. Find the profit percent.

$A$ person purchases $8$ pens for ₹ $10$ and sells $10$ pens for ₹ $8$. How much profit or loss percentage does he make?