A coin bank contains some twenty-cent and fifty-cent coins in the ratio of 4 : 5. When 16 fifty-cent coins were taken out and replaced by some twenty-cent coins, the ratio became 8 : 7. The total value of the twenty-cent coins added was the same as the total value of the fifty-cent coins taken out. Find the sum of money in the coin box.

	Make p the same (1)x7 = (3)	20-cent (1)	50-cent (2)	Make p the same (2)x8 = (4)
Before	28 u	4 u	5 u	40 u
Change	+ 280	+ 40	- 16	- 128
After	56 p	8 p	7 p	56 p

Value of 50-cent coins taken out
= 16 x 0.50
= $8

Number of 20-cent coins put in
= 8 ÷ 0.20
= 40

(3) = (4)
40 u - 128 = 28 u + 280
40 u - 28 u = 280 + 128
12 u = 408

1 u = 408 ÷ 12 = 34

Number of 20-cent coins at first
= 4 u
= 4 x 34
= 136

Number of 50-cent coins at first
= 5 u
= 5 x 34
= 170

Sum of money in the coin box
= 136 x 0.20 + 170 x 0.50
= 27.20 + 85.00
= $112.20

Answer(s): $112.20