2 stickers and 1 marble cost $9.30.
1 sticker and 2 marbles cost $10.20.
- 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 = 10.20 --- (2)
(1) + (2)
3 stickers + 3 marbles = 9.30 + 10.20
3 stickers + 3 marbles = 19.50 --- (3)
(3)
÷ 3
3 stickers + 3 marbles = 19.50
1 sticker + 1 marble = 19.50 ÷ 3
1 sticker + 1 marble = 6.50 --- (4)
Cost of 1 sticker and 1 marble = $6.50
(b)
(2) - (4)
(1 sticker + 2 marbles) - (1 sticker + 1 marble) = 10.20 - 6.50
1 sticker - 1 sticker + 2 marbles - 1 marble = 3.70
1 marble = 3.70
Cost of 1 marble = $3.70
(c)
Substitute 1 marble = 3.70 into (4).
1 sticker + 1 marble = 6.50
1 sticker + 3.70 = 6.50
1 sticker = 6.50 - 3.70 = 2.80
Cost of 1 sticker = $2.80
(d)
(4)
x 9 1 sticker + 1 marble = 6.50
9 x (1 sticker + 1 marble) = 9 x 6.50
9 stickers + 9 marbles = 58.50
Cost of 9 stickers and 9 marbles = $58.50
Answer(s): (a) $6.50; (b) $3.70; (c) $2.80; (d) $58.50