A sticker, a marble and a bead costs $8.30 altogether.
The sticker costs $1.10 less than the marble.
The bead costs $2.50 more than the marble.
How much do 2 beads cost?
Choose the cheapest item to be 1 u.
The sticker costs $1.10 less than the marble.
The cheapest item is the sticker.

Cost of the sticker = 1 u
Cost of the marble = 1 u + 1.10
Cost of the bead = 1 u + 1.10 + 2.50 = 1 u + 3.60

Total cost of the sticker, the marble and the bead
= 1 u + 1 u + 1.10 + 1 u + 3.60
= 1 u + 1 u + 1 u + 1.10 + 3.60
= 3 u + 4.7

3 u + 4.70 = 8.30
3 u = 8.30 - 4.70
3 u = 3.60

1 u = 3.60 ÷ 3 = 1.20

Cost of 2 beads
= 2 x (1 u + 3.60)
= 2 x (1.20 + 3.60)
= 2 x 4.80
= $9.60

Answer(s): $9.60