If Erika gives Charlie $16, the amount of money she has will be 30% of his. If Charlie gives Erika $131, he will have the same amount of money as her. How much money did each of them have?
(a) Charlie
(b) Erika

	Case 1		Case 2
	Charlie	Erika	Charlie	Erika
Before	10 u - 16	3 u + 16	6.5 u + 131	6.5 u - 131
Change	+ 16	- 16	- 131	+ 131
After	10 u	3 u	6.5 u	6.5 u

(a)
30% = ³⁰₁₀₀ = ³₁₀

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

In Case 2, when Charlie gives to Erika, there is an internal transfer of money from Charlie to Erika. 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 Erika and Charlie have
= 10 u + 3 u
= 13 u

Amount that Erika and Charlie each has in the end for Case 2
= 13 u ÷ 2
= 6.5 u

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

10 u - 16 = 6.5 u + 131
10 u - 6.5 u = 131 + 16
3.5 u = 147 

1 u = 147 ÷ 3.5 = 42

Amount that Charlie has
= 10 u - 16
= 10 x 42 - 16
= 420 - 16
= $404 

(b)
Amount that Erika has
= 3 u + 16
= 3 x 42 + 16
= 126 + 16
= $142

Answer(s): (a) $404; (b) $142