Question

Mr Cobb says that increasing something by 10% then decreasing it by 10% will just give you the original amount. Mr Pathuis says the new amount will be bigger. Mr Drake says the new amount will be smaller. Who is right and why?​

Answer 1

Mr Drake Is correct

Explanation:

When you increase something by 10%, you multiply the original value by 1.1. When you decrease it by 10%, you multiply the increased value by 0.9. So the final amount is:

original value x 1.1 x 0.9 = 0.99 x original value

Therefore, the new amount will be slightly smaller than the original amount, and Mr. Drake is correct.

Answer 2

Mr Drake is right.

Explanation:

Because you first decreased it by 10% of the ORIGINAL value.

You then increased it by 10% of the DECREASED value.

The percentages are the same percentages, but on different base amounts.

Simple example:

$100 decreased by 10% of $100 ($10) is $90.

$90 increased by 10% of $90 ($9) is $99.