If Mary gives Fabian $30, the amount of money she has will be 25% of his. If Fabian gives Mary $12, he will have the same amount of money as her. How much money did each of them have?
(a) Fabian
(b) Mary

	Case 1		Case 2
	Fabian	Mary	Fabian	Mary
Before	4 u - 30	1 u + 30	2.5 u + 12	2.5 u - 12
Change	+ 30	- 30	- 12	+ 12
After	4 u	1 u	2.5 u	2.5 u

(a)
25% = ²⁵₁₀₀ = ¹₄

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

In Case 2, when Fabian gives to Mary, there is an internal transfer of money from Fabian to Mary. 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 Mary and Fabian have
= 4 u + 1 u
= 5 u

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

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

4 u - 30 = 2.5 u + 12
4 u - 2.5 u = 12 + 30
1.5 u = 42 

1 u = 42 ÷ 1.5 = 28

Amount that Fabian has
= 4 u - 30
= 4 x 28 - 30
= 112 - 30
= $82 

(b)
Amount that Mary has
= 1 u + 30
= 1 x 28 + 30
= 28 + 30
= $58

Answer(s): (a) $82; (b) $58