In a book shop, the number of highlighters was ¹₂ of the total number of highlighters and correction tapes together. Jenson sold the highlighters and correction tapes in sets of 1 highlighter and 10 correction tapes. After selling all the correction tapes, he still had 36 highlighters left. How many correction tapes were in the book shop at first?

	Highlighters	Correction Tapes
Before	1x10 = 10 u	1x10 = 10 u
Change	- 1x1 =  - 1 u	- 10x1 = - 10 u
After	36	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 10 is 10.

Number of highlighters sold
= 10 u - 1 u
= 9 u

9 u = 36

1 u = 36 ÷ 9 = 4

Number of correction tapes at first
= 10 u
= 10 x 4
= 40

Answer(s): 40