Oscar saved some 20-cent coins and $5 notes in his coin box. The total value of the 20-cent coins to the total value of the $5 notes he had was in the ratio 1 : 3. After $75 worth of 20-cent coins and an equal value of $5 notes were added to the coin box, the ratio of the total value of 20-cent coins to the total value of $5 notes became 8 : 9. How many of each type did Oscar have in the end?

1. 20-cent coins?
2. $5 notes?

	Value of 20-cent	Value of $5	Difference in  value
Before	1x1 = 1 u	3x1 = 3 u	2x1 = 2 u
Change	+ 75	+ 75
After	8x2 = 16 u	9x2 = 18 u	1x2 =  2 u

(a)
The difference in values between 20-cent and $5 remains unchanged. Make the difference in value the same. LCM of 2 and 1 is 2.

Increase in the value of 20-cent coins after more were added
= 16 u - 1 u
= 15 u

15 u = 75

1 u = 75 ÷ 15 = 5

Value of 20-cent coins in the end
= 16 u
= 16 x 5
= $80

100¢ = $1
20¢ = $0.20 

Number of 20-cent coins in the end
= 80 ÷ 0.20
= 400

(b)
Value of $5 notes in the end
= 18 u
= 18 x 5
= $90

Number of $5 notes in the end
= 90 ÷ 5
= 18

Answer(s): (a) 400; (b) 18