If Zoe gives Justin $30, the amount of money she has will be 25% of his. If Justin gives Zoe $3, he will have the same amount of money as her. How much money did each of them have?
(a) Justin
(b) Zoe

	Case 1		Case 2
	Justin	Zoe	Justin	Zoe
Before	4 u - 30	1 u + 30	2.5 u + 3	2.5 u - 3
Change	+ 30	- 30	- 3	+ 3
After	4 u	1 u	2.5 u	2.5 u

(a)
25% = ²⁵₁₀₀ = ¹₄

In Case 1, when Zoe gives to Justin, there is an internal transfer of money from Zoe to Justin.  The total amount that both have remains the same.

In Case 2, when Justin gives to Zoe, there is an internal transfer of money from Justin to Zoe. The total amount that both have remains the same.

The total amount that both have in Case 1 and Case 2 are the same.

Total amount that Zoe and Justin have
= 4 u + 1 u
= 5 u

Amount that Zoe and Justin each has in the end for Case 2
= 5 u ÷ 2
= 2.5 u

Amount that Justin has at first is the same in Case 1 and Case 2.

4 u - 30 = 2.5 u + 3
4 u - 2.5 u = 3 + 30
1.5 u = 33 

1 u = 33 ÷ 1.5 = 22

Amount that Justin has
= 4 u - 30
= 4 x 22 - 30
= 88 - 30
= $58 

(b)
Amount that Zoe has
= 1 u + 30
= 1 x 22 + 30
= 22 + 30
= $52

Answer(s): (a) $58; (b) $52