An article bought for 400 is sold for 500. The profit per cent is:

1. The profit in rupees is 500 - 400 = 100. 2. Profit per cent is always taken on the cost price. 3. So it is 100 / 400 x 100. 4. That gives 25 per cent. 5. Dividing by the sale price would give 20 per cent, which is the standard trap on this question. _Source: syllabus Maths, Ch 7 'Comparing Quantities', S7.1 Recalling Ratios and Percentages_