If Wendy gives Mark $35, the amount of money she has will be 25% of his. If Mark gives Wendy $31, he will have the same amount of money as her. How much money did each of them have?
(a) Mark
(b) Wendy

	Case 1		Case 2
	Mark	Wendy	Mark	Wendy
Before	4 u - 35	1 u + 35	2.5 u + 31	2.5 u - 31
Change	+ 35	- 35	- 31	+ 31
After	4 u	1 u	2.5 u	2.5 u

(a)
25% = ²⁵₁₀₀ = ¹₄

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

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

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

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

4 u - 35 = 2.5 u + 31
4 u - 2.5 u = 31 + 35
1.5 u = 66 

1 u = 66 ÷ 1.5 = 44

Amount that Mark has
= 4 u - 35
= 4 x 44 - 35
= 176 - 35
= $141 

(b)
Amount that Wendy has
= 1 u + 35
= 1 x 44 + 35
= 44 + 35
= $79

Answer(s): (a) $141; (b) $79