Peter and Charlie had 93 notebooks together. Charlie had 3 less notebooks than Peter. Both of them sold some of their notebooks. Charlie sold 20% more notebooks than what Peter sold. In the end, Charlie had half as many notebooks left as Peter. How many notebooks had Charlie left?

	Peter (1)	Charlie (2)	Make p the same (2)x2 = (3)
Comparing Peter and Charlie at first	3 more
Before	48	45	90
Change	- 5 u	- 6 u	- 12 u
After	2 p	1 p	2 p

Number of notebooks that Charlie had at first
= (93 - 3) ÷ 2
= 90 ÷ 2
= 45

Number of notebooks that Peter had at first
= 45 + 3
= 48

Number of notebooks that Charlie sold in percent
= 100% + 20%
= 120%

120% = ¹²⁰₁₀₀ = ⁶₅

Make p the same.

(1) = (3)
48 - 5 u = 90 - 12 u
12 u - 5 u = 90 - 48
7 u = 42

1 u = 42 ÷ 7 = 6

Number of notebooks that Charlie had left
= 45 - 6 u
= 45 - 6 x 6
= 45 - 36
= 9

Answer(s): 9