Luis, Cody and Lee had some stamps in the ratio of 3 : 4 : 7. Lee gave 50% of his stamps to Luis and Cody. As a result, Luis had the same number of stamps as Cody and Lee had 21 fewer stamps than Luis.

1. What was the percentage increase in Luis's stamps after receiving from Lee?
2. How many stamps did Cody have at first?

Luis	Cody	Lee	Total
3 u	4 u	7 u	14 u
+ 3.5 u		- 3.5 u
5.25 u	5.25 u	3.5 u	14 u

(a)
Number of stamps that Lee gave away
= 50% x 7
= ⁵⁰₁₀₀ x 7
= 3.5 u

Number of stamps that Luis and Cody each had in the end
= (14 u - 3.5 u) ÷ 2
= 10.5 u ÷ 2
= 5.25 u

Increase in the number of stamps that Luis had
= 5.25 u - 3 u
= 2.25 u

Percentage increase in Luis's stamps after receiving from Lee
= ^2.25₃ x 100%
= 75%

(b)
5.25 u = 3.5 u + 21
5.25 u - 3.5 u = 21
1.75 u = 21

1 u = 21 ÷ 1.75 = 12

Number of stamps that Cody had at first
= 4 u
= 4 x 12
= 48

Answer(s): (a) 75%; (b) 48