2 marbles and 1 sticker cost $7.50.
1 marble and 2 stickers cost $7.80.
- 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 9 marbles and 9 stickers.
(a)
2 marbles + 1 sticker = 7.50 --- (1)
1 marble + 2 stickers = 7.80 --- (2)
(1) + (2)
3 marbles + 3 stickers = 7.50 + 7.80
3 marbles + 3 stickers = 15.30 --- (3)
(3)
÷ 3
3 marbles + 3 stickers = 15.30
1 marble + 1 sticker = 15.30 ÷ 3
1 marble + 1 sticker = 5.10 --- (4)
Cost of 1 marble and 1 sticker = $5.10
(b)
(2) - (4)
(1 marble + 2 stickers) - (1 marble + 1 marble) = 7.80 - 5.10
1 marble - 1 marble + 2 stickers - 1 sticker = 2.70
1 sticker = 2.70
Cost of 1 sticker = $2.70
(c)
Substitute 1 sticker = 2.70 into (4).
1 marble + 1 sticker = 5.10
1 marble + 2.70 = 5.10
1 marble = 5.10 - 2.70 = 2.40
Cost of 1 marble = $2.40
(d)
(4)
x 9 1 marble + 1 sticker = 5.10
9 x (1 marble + 1 marble) = 9 x 5.10
9 marbles + 9 stickers = 45.90
Cost of 9 marbles and 9 stickers = $45.90
Answer(s): (a) $5.10; (b) $2.70; (c) $2.40; (d) $45.90