Oliver, Cody and Justin had some erasers in the ratio of 6 : 7 : 13. Justin gave 40% of his erasers to Oliver and Cody. As a result, Oliver had the same number of erasers as Cody and Justin had 13 fewer erasers than Oliver.

1. What was the percentage increase in Oliver's erasers after receiving from Justin?
2. How many erasers did Cody have at first?

Oliver	Cody	Justin	Total
6 u	7 u	13 u	26 u
+ 5.2 u		- 5.2 u
9.1 u	9.1 u	7.8 u	26 u

(a)
Number of erasers that Justin gave away
= 40% x 13
= ⁴⁰₁₀₀ x 13
= 5.2 u

Number of erasers that Oliver and Cody each had in the end
= (26 u - 7.8 u) ÷ 2
= 18.2 u ÷ 2
= 9.1 u

Increase in the number of erasers that Oliver had
= 9.1 u - 6 u
= 3.1 u

Percentage increase in Oliver's erasers after receiving from Justin
= ^3.1₆ x 100%
= 51.666666666667%

(b)
9.1 u = 7.8 u + 13
9.1 u - 7.8 u = 13
1.3 u = 13

1 u = 13 ÷ 1.3 = 10

Number of erasers that Cody had at first
= 7 u
= 7 x 10
= 70

Answer(s): (a) 51.666666666667%; (b) 70