The average number of stickers that Charlie and Bryan have is 20.
The average number of stickers that Charlie and Adam have is 50.
The number of stickers that Bryan has is ²₇ as many as Adam.

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

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

Number of stickers that Charlie and Adam has
= 2 x 50
= 100

Number of stickers that Bryan has = 2 u
Number of stickers that Adam has = 7 u

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


C + B = 40
C + 2 u = 40 --- (1)

C + A = 100
C + 7 u = 100 --- (2)

(2) - (1)
(C + 7 u) - (C + 2 u ) = 100 - 40
C + 7 u - C - 2 u = 60
C - C + 7 u - 2 u = 60

5 u = 60

1 u = 60 ÷ 5 = 12

Substitute 1 u = 12 into (1).
C + 2 x 12 = 40
C + 24 = 40
C = 40 - 24 = 16

Number of stickers that Charlie has = 16

(b)
Number of stickers that Bryan has
= 2 u
= 2 x 12
= 24

(c)
Number of stickers that Adam has
= 7 u
= 7 x 12
= 84

Answer(s): (a) 16; (b) 24; (c) 84