If Erika gives David $16, the amount of money she has will be 40% of his. If David gives Erika $26, he will have the same amount of money as her. How much money did each of them have?
(a) David
(b) Erika

	Case 1		Case 2
	David	Erika	David	Erika
Before	5 u - 16	2 u + 16	3.5 u + 26	3.5 u - 26
Change	+ 16	- 16	- 26	+ 26
After	5 u	2 u	3.5 u	3.5 u

(a)
40% = ⁴⁰₁₀₀ = ²₅

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

In Case 2, when David gives to Erika, there is an internal transfer of money from David 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 David have
= 5 u + 2 u
= 7 u

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

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

5 u - 16 = 3.5 u + 26
5 u - 3.5 u = 26 + 16
1.5 u = 42 

1 u = 42 ÷ 1.5 = 28

Amount that David has
= 5 u - 16
= 5 x 28 - 16
= 140 - 16
= $124 

(b)
Amount that Erika has
= 2 u + 16
= 2 x 28 + 16
= 56 + 16
= $72

Answer(s): (a) $124; (b) $72