4 stickers and 1 marble cost $22.10.
1 sticker and 4 marbles cost $16.40.
- 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)
4 stickers + 1 marble = 22.10 --- (1)
1 sticker + 4 marbles = 16.40 --- (2)
(1) + (2)
5 stickers + 5 marbles = 22.10 + 16.40
5 stickers + 5 marbles = 38.50 --- (3)
(3)
÷ 55 stickers + 5 marbles = 38.50
1 sticker + 1 marble = 38.50 ÷ 5
1 sticker + 1 marble = 7.70 --- (4)
(b)
(2) - (4)
(1 sticker + 4 marbles) - (1 sticker + 1 marble) = 16.40 - 7.70
1 sticker - 1 sticker + 4 marbles - 1 marble = 8.70
3 marbles = 8.70
1 marble = 8.70 ÷ 3 = 2.90
Cost of 1 marble = $2.90
(c)
Substitute 1 marble = 2.90 into (4).
1 sticker + 1 marble = 7.70
1 sticker + 2.90 = 7.70
1 sticker = 7.70 - 2.90 = 4.80
Cost of 1 sticker = $4.80
(d)
(4)
x 9 1 sticker + 1 marble = 7.70
9 x (1 sticker + 1 marble) = 9 x 7.70
9 stickers + 9 marbles = 69.30
Cost of 9 stickers and 9 marbles = $69.30
Answer(s): (a) $7.70; (b) $2.90; (c) $4.80; (d) $69.30