In a book shop, the number of staplers was ³₄ of the total number of staplers and correction tapes together. Billy sold the staplers and correction tapes in sets of 3 staplers and 7 correction tapes. After selling all the correction tapes, he still had 90 staplers left. How many correction tapes were in the book shop were sold?

	Staplers	Correction Tapes
Before	3x7 = 21 u	1x7 = 7 u
Change	- 3x1 =  - 3 u	- 7x1 = - 7 u
After	90	0

Since all the correction tapes were sold, the number of correction tapes at first and the number of correction tapes sold were the same.  Make the number of correction tapes at first and sold the same.  LCM of 1 and 7 is 7.

Number of staplers sold
= 21 u - 3 u
= 18 u

18 u = 90

1 u = 90 ÷ 18 = 5

Number of correction tapes were sold
= 7 u
= 7 x 5
= 35

Answer(s): 35