David, Ivan and Vincent had some erasers in the ratio of 2 : 3 : 5. Vincent gave 40% of his erasers to David and Ivan. As a result, David had the same number of erasers as Ivan and Vincent had 20 fewer erasers than David.

1. What was the percentage increase in David's erasers after receiving from Vincent?
2. How many erasers did Ivan have at first?

David	Ivan	Vincent	Total
2 u	3 u	5 u	10 u
+ 2 u		- 2 u
3.5 u	3.5 u	3 u	10 u

(a)
Number of erasers that Vincent gave away
= 40% x 5
= ⁴⁰₁₀₀ x 5
= 2 u

Number of erasers that David and Ivan each had in the end
= (10 u - 3 u) ÷ 2
= 7 u ÷ 2
= 3.5 u

Increase in the number of erasers that David had
= 3.5 u - 2 u
= 1.5 u

Percentage increase in David's erasers after receiving from Vincent
= ^1.5₂ x 100%
= 75%

(b)
3.5 u = 3 u + 20
3.5 u - 3 u = 20
0.5 u = 20

1 u = 20 ÷ 0.5 = 40

Number of erasers that Ivan had at first
= 3 u
= 3 x 40
= 120

Answer(s): (a) 75%; (b) 120