Question

Ally collects stickers as a hobby. She gives her sister of her stickers. She then gives her cousinof the remainder. Ally says that she has of the stickers in the end because1-1/5-1/5= 3/5

Explain why Ally's reasoning is incorrect. What should the correct answer be?

Answer 1

Ally's reasoning is incorrect because she double-counts a portion of the stickers.

First step: She gives away 1/5 of her stickers to her sister. This means she has 4/5 remaining.

Second step: She then gives away 1/5 of the remaining stickers (which is 4/5) to her cousin. This is not the same as giving away 1/5 of the original number of stickers.

Double-counting: By giving away 1/5 of the remaining stickers, Ally essentially counts the stickers she gave to her sister again. This is because the remaining 4/5 stickers already include the portion she gave to her sister.

Therefore, Ally's final calculation of 3/5 is inaccurate.

Correct calculation:

Instead of subtracting 1/5 twice, we should subtract the total portion given away once: 4/5 (remaining) - 1/5 (given to cousin) = 3/5.

So, Ally actually has 3/5 of her stickers left, not 1/5.