Zara used ⁵₇ of her black stickers and ²₅ of her purple stickers to decorate her diary. In the end, she had an equal number of black stickers and purple stickers left. Given that Zara had a total of 124 black and purple stickers at first, how many purple stickers did she use to decorate the diary?

	Black stickers	Purple stickers
Before	7x3 = 21 u	5x2 = 10 u
Change	- 5x3 = - 15 u	- 2x2 = - 4 u
After	2x3 = 6 u	3x2 = 6 u

The number of black stickers and purple stickers in the end is the same.  Make the number of black stickers and purple stickers in the end the same.  LCM of 2 and 3 is 6.

Total number of stickers that Zara used to decorate the diary
= 21 u + 10 u
= 31 u

31 u = 124

1 u = 124 ÷ 31 = 4

Number of purple stickers that Zara used to decorate the diary
= 4 u
= 4 x 4
= 16

Answer(s): 16