Adam pays $25.20 for a marble, a bead and a sticker.
The marble costs $2.50 less than the bead.
The bead costs $1.90 less than the sticker.
What is the cost of 5 marbles less than 8 stickers?
Choose the cheapest item to be 1 u.

Cost of the marble = 1 u
Cost of the bead = 1 u + 2.50
Cost of the sticker = 1 u + 2.50 + 1.90 = 1 u + 4.40

Total cost of the marble, the bead and the sticker
= 1 u + 1 u + 2.50 + 1 u + 4.40
= 3 u + 6.90

3 u + 6.90 = 25.20
3 u = 25.20 - 6.90
3 u = 18.30

1 u = 18.30 ÷ 3 = 6.10

Cost of 5 marbles less than 8 stickers 
= 8 x (1 u + 4.40) - 5 x 1 u
= 8 u + 35.20 - 5 u
= 3 u + 35.20
= 3 x 6.10 + 35.20
= 18.30 + 35.20
= $53.50

Answer(s): $53.50