Tom saved some 10-cent coins and $1 notes in his coin box. The total value of the 10-cent coins to the total value of the $1 notes he had was in the ratio 4 : 7. After $12 worth of 10-cent coins and an equal value of $1 notes were added to the coin box, the ratio of the total value of 10-cent coins to the total value of $1 notes became 2 : 3. How many of each type did Tom have in the end?

1. 10-cent coins?
2. $1 notes?

	Value of 10-cent	Value of $1	Difference in  value
Before	4x1 = 4 u	7x1 = 7 u	3x1 = 3 u
Change	+ 12	+ 12
After	2x3 = 6 u	3x3 = 9 u	1x3 =  3 u

(a)
The difference in values between 10-cent and $1 remains unchanged. Make the difference in value the same. LCM of 3 and 1 is 3.

Increase in the value of 10-cent coins after more were added
= 6 u - 4 u
= 2 u

2 u = 12

1 u = 12 ÷ 2 = 6

Value of 10-cent coins in the end
= 6 u
= 6 x 6
= $36

100¢ = $1
10¢ = $0.10 

Number of 10-cent coins in the end
= 36 ÷ 0.10
= 360

(b)
Value of $1 notes in the end
= 9 u
= 9 x 6
= $54

Number of $1 notes in the end
= 54 ÷ 1
= 54

Answer(s): (a) 360; (b) 54