5 marbles and 1 sticker cost $20.90.
1 marble and 5 stickers cost $15.70.
- 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)
5 marbles + 1 sticker = 20.90 --- (1)
1 marble + 5 stickers = 15.70 --- (2)
(1) + (2)
6 marbles + 6 stickers = 20.90 + 15.70
6 marbles + 6 stickers = 36.60 --- (3)
(3)
÷ 66 marbles + 6 stickers = 36.60
1 marble + 1 sticker = 36.60 ÷ 6
1 marble + 1 sticker = 6.10 --- (4)
(b)
(2) - (4)
(1 marble + 5 stickers) - (1 marble + 1 marble) = 15.70 - 6.10
1 marble - 1 marble + 5 stickers - 1 sticker = 9.60
4 stickers = 9.60
1 sticker = 9.60 ÷ 4 = 2.40
Cost of 1 sticker = $2.40
(c)
Substitute 1 sticker = 2.40 into (4).
1 marble + 1 sticker = 6.10
1 marble + 2.40 = 6.10
1 marble = 6.10 - 2.40 = 3.70
Cost of 1 marble = $3.70
(d)
(4)
x 7 1 marble + 1 sticker = 6.10
7 x (1 marble + 1 marble) = 7 x 6.10
7 marbles + 7 stickers = 42.70
Cost of 7 marbles and 7 stickers = $42.70
Answer(s): (a) $6.10; (b) $2.40; (c) $3.70; (d) $42.70