Question

Z decreased by 20% and then the result increased by 20%

Answer 1

Assume that the number is 100. Then, 20% of 100 is 20×100100 = 20. Increasing 100 by 20% means increasing 100 by 20 and the resultant number is 120.

Now the new number is 120. 20% of 120 is 20×120100 = 120/5 = 24. Thus decreasing 120 by 20% means same as subtracting 24 from 120 and the resultant number will be 120 — 24 = 96.

Since 96 is less than 100, the original number, net decrease

=100−96100×100

=4100×100

=4

Thus the net decrease is 4%. It is true for all other numbers.

Explanation: