3 marbles and 1 sticker cost $7.90.
1 marble and 3 stickers cost $14.90.
- 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 = 7.90 --- (1)
1 marble + 3 stickers = 14.90 --- (2)
(1) + (2)
4 marbles + 4 stickers = 7.90 + 14.90
4 marbles + 4 stickers = 22.80 --- (3)
(3)
÷ 44 marbles + 4 stickers = 22.80
1 marble + 1 sticker = 22.80 ÷ 4
1 marble + 1 sticker = 5.70 --- (4)
(b)
(2) - (4)
(1 marble + 3 stickers) - (1 marble + 1 marble) = 14.90 - 5.70
1 marble - 1 marble + 3 stickers - 1 sticker = 9.20
2 stickers = 9.20
1 sticker = 9.20 ÷ 2 = 4.60
Cost of 1 sticker = $4.60
(c)
Substitute 1 sticker = 4.60 into (4).
1 marble + 1 sticker = 5.70
1 marble + 4.60 = 5.70
1 marble = 5.70 - 4.60 = 1.10
Cost of 1 marble = $1.10
(d)
(4)
x 7 1 marble + 1 sticker = 5.70
7 x (1 marble + 1 marble) = 7 x 5.70
7 marbles + 7 stickers = 39.90
Cost of 7 marbles and 7 stickers = $39.90
Answer(s): (a) $5.70; (b) $4.60; (c) $1.10; (d) $39.90