Question

The cost of a transistor decreases from rupees 400 to rupees 380 what is the percentage of decrease

Answer 1

Percentage of decrease = [(past price)-(present price)]/(past price) * 100

                                        = (400-380)/400 *100

                                        = 5%

Answer 2

How the answer is come.

If we subtract: 400- 380 the answer is 20.

In yours you did (400-380)/400*100 so after the slash where the 400 comes