4 marbles and 1 bead cost $8.70.
1 marble and 4 beads cost $10.80.

1. Find the cost of 1 marble and 1 bead.
2. Find the cost of 1 bead.
3. Find the cost of 1 marble.
4. Find the cost of 8 marbles and 8 beads.

(a)
4 marbles + 1 bead = 8.70 --- (1)
1 marble + 4 beads = 10.80 --- (2)

(1) + (2)
5 marbles + 5 beads = 8.70 + 10.80
5 marbles + 5 beads = 19.50 --- (3)

(3) _{÷ 5}
5 marbles + 5 beads = 19.50
1 marble + 1 bead = 19.50 ÷ 5
1 marble + 1 bead = 3.90 --- (4)

(b)
(2) - (4)
(1 marble + 4 beads) - (1 marble + 1 marble) = 10.80 - 3.90
1 marble - 1 marble + 4 beads - 1 bead = 6.90
3 beads = 6.90
1 bead = 6.90 ÷ 3 = 2.30

Cost of 1 bead = $2.30

(c)
Substitute 1 bead = 2.30 into (4).
1 marble + 1 bead = 3.90
1 marble + 2.30 = 3.90
1 marble = 3.90 - 2.30 = 1.60

Cost of 1 marble = $1.60

(d)
(4) _{x 8}
1 marble + 1 bead = 3.90
8 x (1 marble + 1 marble) = 8 x 3.90
8 marbles + 8 beads = 31.20

Cost of 8 marbles and 8 beads = $31.20

Answer(s): (a) $3.90; (b) $2.30; (c) $1.60; (d) $31.20