4 marbles and 1 bead cost $12.90.
1 marble and 4 beads cost $15.60.
- Find the cost of 1 marble and 1 bead.
- Find the cost of 1 bead.
- Find the cost of 1 marble.
- Find the cost of 9 marbles and 9 beads.
(a)
4 marbles + 1 bead = 12.90 --- (1)
1 marble + 4 beads = 15.60 --- (2)
(1) + (2)
5 marbles + 5 beads = 12.90 + 15.60
5 marbles + 5 beads = 28.50 --- (3)
(3)
÷ 55 marbles + 5 beads = 28.50
1 marble + 1 bead = 28.50 ÷ 5
1 marble + 1 bead = 5.70 --- (4)
(b)
(2) - (4)
(1 marble + 4 beads) - (1 marble + 1 marble) = 15.60 - 5.70
1 marble - 1 marble + 4 beads - 1 bead = 9.90
3 beads = 9.90
1 bead = 9.90 ÷ 3 = 3.30
Cost of 1 bead = $3.30
(c)
Substitute 1 bead = 3.30 into (4).
1 marble + 1 bead = 5.70
1 marble + 3.30 = 5.70
1 marble = 5.70 - 3.30 = 2.40
Cost of 1 marble = $2.40
(d)
(4)
x 9 1 marble + 1 bead = 5.70
9 x (1 marble + 1 marble) = 9 x 5.70
9 marbles + 9 beads = 51.30
Cost of 9 marbles and 9 beads = $51.30
Answer(s): (a) $5.70; (b) $3.30; (c) $2.40; (d) $51.30