A coin bank contains some ten-cent and fifty-cent coins in the ratio of 4 : 5. When 12 fifty-cent coins were taken out and replaced by some ten-cent coins, the ratio became 9 : 8. The total value of the ten-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)x8 = (3)	10-cent (1)	50-cent (2)	Make p the same (2)x9 = (4)
Before	32 u	4 u	5 u	45 u
Change	+ 480	+ 60	- 12	- 108
After	72 p	9 p	8 p	72 p

Value of 50-cent coins taken out
= 12 x 0.50
= $6

Number of 10-cent coins put in
= 6 ÷ 0.10
= 60

(3) = (4)
45 u - 108 = 32 u + 480
45 u - 32 u = 480 + 108
28 u = 588

1 u = 588 ÷ 28 = 21

Number of 10-cent coins at first
= 4 u
= 4 x 21
= 84

Number of 50-cent coins at first
= 5 u
= 5 x 21
= 105

Sum of money in the coin box
= 84 x 0.10 + 105 x 0.50
= 8.40 + 52.50
= $60.90

Answer(s): $60.90