If Joelle gives Bobby $15, the amount of money she has will be 75% of his. If Bobby gives Joelle $5, he will have the same amount of money as her. How much money did each of them have?
(a) Bobby
(b) Joelle

	Case 1		Case 2
	Bobby	Joelle	Bobby	Joelle
Before	4 u - 15	3 u + 15	3.5 u + 5	3.5 u - 5
Change	+ 15	- 15	- 5	+ 5
After	4 u	3 u	3.5 u	3.5 u

(a)
75% = ⁷⁵₁₀₀ = ³₄

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

In Case 2, when Bobby gives to Joelle, there is an internal transfer of money from Bobby to Joelle. 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 Joelle and Bobby have
= 4 u + 3 u
= 7 u

Amount that Joelle and Bobby each has in the end for Case 2
= 7 u ÷ 2
= 3.5 u

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

4 u - 15 = 3.5 u + 5
4 u - 3.5 u = 5 + 15
0.5 u = 20 

1 u = 20 ÷ 0.5 = 40

Amount that Bobby has
= 4 u - 15
= 4 x 40 - 15
= 160 - 15
= $145 

(b)
Amount that Joelle has
= 3 u + 15
= 3 x 40 + 15
= 120 + 15
= $135

Answer(s): (a) $145; (b) $135