3 stickers and 1 marble cost $6.90.
1 sticker and 3 marbles cost $5.50.
- 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 9 stickers and 9 marbles.
(a)
3 stickers + 1 marble = 6.90 --- (1)
1 sticker + 3 marbles = 5.50 --- (2)
(1) + (2)
4 stickers + 4 marbles = 6.90 + 5.50
4 stickers + 4 marbles = 12.40 --- (3)
(3)
÷ 44 stickers + 4 marbles = 12.40
1 sticker + 1 marble = 12.40 ÷ 4
1 sticker + 1 marble = 3.10 --- (4)
(b)
(2) - (4)
(1 sticker + 3 marbles) - (1 sticker + 1 marble) = 5.50 - 3.10
1 sticker - 1 sticker + 3 marbles - 1 marble = 2.40
2 marbles = 2.40
1 marble = 2.40 ÷ 2 = 1.20
Cost of 1 marble = $1.20
(c)
Substitute 1 marble = 1.20 into (4).
1 sticker + 1 marble = 3.10
1 sticker + 1.20 = 3.10
1 sticker = 3.10 - 1.20 = 1.90
Cost of 1 sticker = $1.90
(d)
(4)
x 9 1 sticker + 1 marble = 3.10
9 x (1 sticker + 1 marble) = 9 x 3.10
9 stickers + 9 marbles = 27.90
Cost of 9 stickers and 9 marbles = $27.90
Answer(s): (a) $3.10; (b) $1.20; (c) $1.90; (d) $27.90