The average number of stickers that Adam and Charlie have is 20.
The average number of stickers that Adam and Bryan have is 40.
The number of stickers that Charlie has is ⁴₉ as many as Bryan.

1. How many stickers does Adam have?
2. How many stickers does Charlie have?
3. How many stickers does Bryan have?

(a)
Number of stickers that Adam and Charlie has
= 2 x 20
= 40

Number of stickers that Adam and Bryan has
= 2 x 40
= 80

Number of stickers that Charlie has = 4 u
Number of stickers that Bryan has = 9 u

Let the number of Adam's stickers be A.
Let the number of Charlie's stickers be C.
Let the number of Bryan's stickers be B.


A + C = 40
A + 4 u = 40 --- (1)

A + B = 80
A + 9 u = 80 --- (2)

(2) - (1)
(A + 9 u) - (A + 4 u ) = 80 - 40
A + 9 u - A - 4 u = 40
A - A + 9 u - 4 u = 40

5 u = 40

1 u = 40 ÷ 5 = 8

Substitute 1 u = 8 into (1).
A + 4 x 8 = 40
A + 32 = 40
A = 40 - 32 = 8

Number of stickers that Adam has = 8

(b)
Number of stickers that Charlie has
= 4 u
= 4 x 8
= 32

(c)
Number of stickers that Bryan has
= 9 u
= 9 x 8
= 72

Answer(s): (a) 8; (b) 32; (c) 72