3 stickers and 1 marble cost $17.50.
1 sticker and 3 marbles cost $14.90.
- 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 = 17.50 --- (1)
1 sticker + 3 marbles = 14.90 --- (2)
(1) + (2)
4 stickers + 4 marbles = 17.50 + 14.90
4 stickers + 4 marbles = 32.40 --- (3)
(3)
÷ 44 stickers + 4 marbles = 32.40
1 sticker + 1 marble = 32.40 ÷ 4
1 sticker + 1 marble = 8.10 --- (4)
(b)
(2) - (4)
(1 sticker + 3 marbles) - (1 sticker + 1 marble) = 14.90 - 8.10
1 sticker - 1 sticker + 3 marbles - 1 marble = 6.80
2 marbles = 6.80
1 marble = 6.80 ÷ 2 = 3.40
Cost of 1 marble = $3.40
(c)
Substitute 1 marble = 3.40 into (4).
1 sticker + 1 marble = 8.10
1 sticker + 3.40 = 8.10
1 sticker = 8.10 - 3.40 = 4.70
Cost of 1 sticker = $4.70
(d)
(4)
x 9 1 sticker + 1 marble = 8.10
9 x (1 sticker + 1 marble) = 9 x 8.10
9 stickers + 9 marbles = 72.90
Cost of 9 stickers and 9 marbles = $72.90
Answer(s): (a) $8.10; (b) $3.40; (c) $4.70; (d) $72.90