$A$ shopkeeper gains the cost of $8$ metres of thread by selling $40$ metres of thread. Find his gain percent.

The marked price of a watch was $Rs. 720$. $A$ man bought the same for $Rs. 550.80$ after getting two successive discounts,the first being $10\%$. What was the second discount rate? (in $\%$)

In these questions,two equations numbered $I$ and $II$ are given. You have to solve both the equations and mark the appropriate option.
$I.$ $3x^2 - 13x + 12 = 0$
$II.$ $2y^2 - 15y + 28 = 0$

The ratio between the selling price and the cost price of an article is $7:5$. What is the ratio between the profit and the cost price of that article?

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......$\%$

$X$ sells two articles for $Rs. 4,000$ each with no loss and no gain in the transaction. If one was sold at a gain of $25\%$, the other is sold at a loss of ........$\%$.