If Abi gives Pierre $39, the amount of money she has will be 25% of his. If Pierre gives Abi $9, he will have the same amount of money as her. How much money did each of them have?
(a) Pierre
(b) Abi

	Case 1		Case 2
	Pierre	Abi	Pierre	Abi
Before	4 u - 39	1 u + 39	2.5 u + 9	2.5 u - 9
Change	+ 39	- 39	- 9	+ 9
After	4 u	1 u	2.5 u	2.5 u

(a)
25% = ²⁵₁₀₀ = ¹₄

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

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

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

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

4 u - 39 = 2.5 u + 9
4 u - 2.5 u = 9 + 39
1.5 u = 48 

1 u = 48 ÷ 1.5 = 32

Amount that Pierre has
= 4 u - 39
= 4 x 32 - 39
= 128 - 39
= $89 

(b)
Amount that Abi has
= 1 u + 39
= 1 x 32 + 39
= 32 + 39
= $71

Answer(s): (a) $89; (b) $71