2 stickers and 1 marble cost $9.30.
1 sticker and 2 marbles cost $8.10.
- Find the cost of 1 sticker and 1 marble.
- Find the cost of 1 marble.
- Find the cost of 1 sticker.
- Find the cost of 9 stickers and 9 marbles.
(a)
2 stickers + 1 marble = 9.30 --- (1)
1 sticker + 2 marbles = 8.10 --- (2)
(1) + (2)
3 stickers + 3 marbles = 9.30 + 8.10
3 stickers + 3 marbles = 17.40 --- (3)
(3)
÷ 3
3 stickers + 3 marbles = 17.40
1 sticker + 1 marble = 17.40 ÷ 3
1 sticker + 1 marble = 5.80 --- (4)
Cost of 1 sticker and 1 marble = $5.80
(b)
(2) - (4)
(1 sticker + 2 marbles) - (1 sticker + 1 marble) = 8.10 - 5.80
1 sticker - 1 sticker + 2 marbles - 1 marble = 2.30
1 marble = 2.30
Cost of 1 marble = $2.30
(c)
Substitute 1 marble = 2.30 into (4).
1 sticker + 1 marble = 5.80
1 sticker + 2.30 = 5.80
1 sticker = 5.80 - 2.30 = 3.50
Cost of 1 sticker = $3.50
(d)
(4)
x 9 1 sticker + 1 marble = 5.80
9 x (1 sticker + 1 marble) = 9 x 5.80
9 stickers + 9 marbles = 52.20
Cost of 9 stickers and 9 marbles = $52.20
Answer(s): (a) $5.80; (b) $2.30; (c) $3.50; (d) $52.20