2 stickers and 1 marble cost $6.10.
1 sticker and 2 marbles cost $6.50.
- 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 7 stickers and 7 marbles.
(a)
2 stickers + 1 marble = 6.10 --- (1)
1 sticker + 2 marbles = 6.50 --- (2)
(1) + (2)
3 stickers + 3 marbles = 6.10 + 6.50
3 stickers + 3 marbles = 12.60 --- (3)
(3)
÷ 3
3 stickers + 3 marbles = 12.60
1 sticker + 1 marble = 12.60 ÷ 3
1 sticker + 1 marble = 4.20 --- (4)
Cost of 1 sticker and 1 marble = $4.20
(b)
(2) - (4)
(1 sticker + 2 marbles) - (1 sticker + 1 marble) = 6.50 - 4.20
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 = 4.20
1 sticker + 2.30 = 4.20
1 sticker = 4.20 - 2.30 = 1.90
Cost of 1 sticker = $1.90
(d)
(4)
x 7 1 sticker + 1 marble = 4.20
7 x (1 sticker + 1 marble) = 7 x 4.20
7 stickers + 7 marbles = 29.40
Cost of 7 stickers and 7 marbles = $29.40
Answer(s): (a) $4.20; (b) $2.30; (c) $1.90; (d) $29.40