4 marbles and 1 sticker cost $21.40.
1 marble and 4 stickers cost $21.10.
- 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)
4 marbles + 1 sticker = 21.40 --- (1)
1 marble + 4 stickers = 21.10 --- (2)
(1) + (2)
5 marbles + 5 stickers = 21.40 + 21.10
5 marbles + 5 stickers = 42.50 --- (3)
(3)
÷ 55 marbles + 5 stickers = 42.50
1 marble + 1 sticker = 42.50 ÷ 5
1 marble + 1 sticker = 8.50 --- (4)
(b)
(2) - (4)
(1 marble + 4 stickers) - (1 marble + 1 marble) = 21.10 - 8.50
1 marble - 1 marble + 4 stickers - 1 sticker = 12.60
3 stickers = 12.60
1 sticker = 12.60 ÷ 3 = 4.20
Cost of 1 sticker = $4.20
(c)
Substitute 1 sticker = 4.20 into (4).
1 marble + 1 sticker = 8.50
1 marble + 4.20 = 8.50
1 marble = 8.50 - 4.20 = 4.30
Cost of 1 marble = $4.30
(d)
(4)
x 7 1 marble + 1 sticker = 8.50
7 x (1 marble + 1 marble) = 7 x 8.50
7 marbles + 7 stickers = 59.50
Cost of 7 marbles and 7 stickers = $59.50
Answer(s): (a) $8.50; (b) $4.20; (c) $4.30; (d) $59.50