If a man were to sell his chair for Rs. 720, he would lose 25%. To gain 25% he should sell it for:

Explanation:-

Let the Cost price of the Chair is X.
SP = X - 25% of X
720 = 0.75X
X = 960.
CP = Rs. 960.
So, To gain 25%, SP would be
= 960 + 25% of 960 =Rs. 1200.

Short-cut
CP of chair = (¹⁰⁰/₇₅)*720 = Rs. 960;
To gain 25%, SP = (¹²⁵/₁₀₀)*960 = Rs. 1200.