A sticker, a marble and a bead costs $9.50 altogether.
The sticker costs $1.40 less than the marble.
The bead costs $2.50 more than the marble.
How much do 3 beads cost?
Choose the cheapest item to be 1 u.
The sticker costs $1.40 less than the marble.
The cheapest item is the sticker.

Cost of the sticker = 1 u
Cost of the marble = 1 u + 1.40
Cost of the bead = 1 u + 1.40 + 2.50 = 1 u + 3.90

Total cost of the sticker, the marble and the bead
= 1 u + 1 u + 1.40 + 1 u + 3.90
= 1 u + 1 u + 1 u + 1.40 + 3.90
= 3 u + 5.3

3 u + 5.30 = 9.50
3 u = 9.50 - 5.30
3 u = 4.20

1 u = 4.20 ÷ 3 = 1.40

Cost of 3 beads
= 3 x (1 u + 3.90)
= 3 x (1.40 + 3.90)
= 3 x 5.30
= $15.90

Answer(s): $15.90