3 marbles and 1 sticker cost $8.20.
1 marble and 3 stickers cost $12.60.
- Find the cost of 1 marble and 1 sticker.
- Find the cost of 1 sticker.
- Find the cost of 1 marble.
- Find the cost of 7 marbles and 7 stickers.
(a)
3 marbles + 1 sticker = 8.20 --- (1)
1 marble + 3 stickers = 12.60 --- (2)
(1) + (2)
4 marbles + 4 stickers = 8.20 + 12.60
4 marbles + 4 stickers = 20.80 --- (3)
(3)
÷ 44 marbles + 4 stickers = 20.80
1 marble + 1 sticker = 20.80 ÷ 4
1 marble + 1 sticker = 5.20 --- (4)
(b)
(2) - (4)
(1 marble + 3 stickers) - (1 marble + 1 marble) = 12.60 - 5.20
1 marble - 1 marble + 3 stickers - 1 sticker = 7.40
2 stickers = 7.40
1 sticker = 7.40 ÷ 2 = 3.70
Cost of 1 sticker = $3.70
(c)
Substitute 1 sticker = 3.70 into (4).
1 marble + 1 sticker = 5.20
1 marble + 3.70 = 5.20
1 marble = 5.20 - 3.70 = 1.50
Cost of 1 marble = $1.50
(d)
(4)
x 7 1 marble + 1 sticker = 5.20
7 x (1 marble + 1 marble) = 7 x 5.20
7 marbles + 7 stickers = 36.40
Cost of 7 marbles and 7 stickers = $36.40
Answer(s): (a) $5.20; (b) $3.70; (c) $1.50; (d) $36.40