Barbara used ⁴₇ of her white stickers and ³₄ of her black stickers to decorate her diary. In the end, she had an equal number of white stickers and black stickers left. Given that Barbara had a total of 57 white and black stickers at first, how many black stickers did she use to decorate the diary?

	White stickers	Black stickers
Before	7x1 = 7 u	4x3 = 12 u
Change	- 4x1 = - 4 u	- 3x3 = - 9 u
After	3x1 = 3 u	1x3 = 3 u

The number of white stickers and black stickers in the end is the same.  Make the number of white stickers and black stickers in the end the same.  LCM of 3 and 1 is 3.

Total number of stickers that Barbara used to decorate the diary
= 7 u + 12 u
= 19 u

19 u = 57

1 u = 57 ÷ 19 = 3

Number of black stickers that Barbara used to decorate the diary
= 9 u
= 9 x 3
= 27

Answer(s): 27