3 stickers and 1 marble cost $15.70.
1 sticker and 3 marbles cost $17.50.
- 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 = 15.70 --- (1)
1 sticker + 3 marbles = 17.50 --- (2)
(1) + (2)
4 stickers + 4 marbles = 15.70 + 17.50
4 stickers + 4 marbles = 33.20 --- (3)
(3)
÷ 44 stickers + 4 marbles = 33.20
1 sticker + 1 marble = 33.20 ÷ 4
1 sticker + 1 marble = 8.30 --- (4)
(b)
(2) - (4)
(1 sticker + 3 marbles) - (1 sticker + 1 marble) = 17.50 - 8.30
1 sticker - 1 sticker + 3 marbles - 1 marble = 9.20
2 marbles = 9.20
1 marble = 9.20 ÷ 2 = 4.60
Cost of 1 marble = $4.60
(c)
Substitute 1 marble = 4.60 into (4).
1 sticker + 1 marble = 8.30
1 sticker + 4.60 = 8.30
1 sticker = 8.30 - 4.60 = 3.70
Cost of 1 sticker = $3.70
(d)
(4)
x 9 1 sticker + 1 marble = 8.30
9 x (1 sticker + 1 marble) = 9 x 8.30
9 stickers + 9 marbles = 74.70
Cost of 9 stickers and 9 marbles = $74.70
Answer(s): (a) $8.30; (b) $4.60; (c) $3.70; (d) $74.70