Ivory had 125 coins. ²₅ were grey and the rest were pink and black. The ratio of the number of pink coins to the number of black coins was 1 : 4. Ivory decided to buy some more grey coins to increase the number of grey coins to half of the total number of coins.

1. How many less pink coins than grey coins did he have at first?
2. How many more grey coins did he have to buy?

Grey coins	Pink coins	Black coins	Total
2x5	3x5
	1x3	4x3
10 u	3 u	12 u	125

	Grey coins	Pink coins	Black coins
Before	10 u	3 u	12 u
Change	+ ?
After	15 u	15 u
Comparing grey, pink and black coins in the end	1	1

(a)
The total number of pink coins and black coins is repeated. Make the total number of pink coins and black coins the same.  LCM of 3 and 5 is 15.

Total number of coins at first
= 10 u + 3 u + 12 u
= 25 u

25 u = 125

1 u = 125 ÷ 25 = 5

Number of less pink coins than grey coins at first
= 10 u - 3 u
= 7 u
= 7 x 5
= 35

(b)
Number of more grey coins that Ivory had to buy
= 15 u - 10 u
= 5 u
= 5 x 5
= 25

Answer(s): (a) 35; (b) 25