A trader sells an article at a profit of 20%. Had he bought it at 10% more and sold it for Rs 700 more, he would have earned a profit of 25%. Find the cost price.

The cost price works out to Rs 4000.

Take CP = x, so first SP = 1.20x.

New CP = 1.10x and the new SP at 25% profit = 1.25 x 1.10x = 1.375x.

This new SP is Rs 700 above the old one: 1.375x = 1.20x + 700.

0.175x = 700, so x = 700 / 0.175 = 4000.

Write both selling prices in terms of CP and equate the gap.