2 stickers and 1 marble cost $6.30.
1 sticker and 2 marbles cost $7.80.
- 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 = 6.30 --- (1)
1 sticker + 2 marbles = 7.80 --- (2)
(1) + (2)
3 stickers + 3 marbles = 6.30 + 7.80
3 stickers + 3 marbles = 14.10 --- (3)
(3)
÷ 3
3 stickers + 3 marbles = 14.10
1 sticker + 1 marble = 14.10 ÷ 3
1 sticker + 1 marble = 4.70 --- (4)
Cost of 1 sticker and 1 marble = $4.70
(b)
(2) - (4)
(1 sticker + 2 marbles) - (1 sticker + 1 marble) = 7.80 - 4.70
1 sticker - 1 sticker + 2 marbles - 1 marble = 3.10
1 marble = 3.10
Cost of 1 marble = $3.10
(c)
Substitute 1 marble = 3.10 into (4).
1 sticker + 1 marble = 4.70
1 sticker + 3.10 = 4.70
1 sticker = 4.70 - 3.10 = 1.60
Cost of 1 sticker = $1.60
(d)
(4)
x 9 1 sticker + 1 marble = 4.70
9 x (1 sticker + 1 marble) = 9 x 4.70
9 stickers + 9 marbles = 42.30
Cost of 9 stickers and 9 marbles = $42.30
Answer(s): (a) $4.70; (b) $3.10; (c) $1.60; (d) $42.30