5 marbles and 1 sticker cost $19.90.
1 marble and 5 stickers cost $15.50.
- 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)
5 marbles + 1 sticker = 19.90 --- (1)
1 marble + 5 stickers = 15.50 --- (2)
(1) + (2)
6 marbles + 6 stickers = 19.90 + 15.50
6 marbles + 6 stickers = 35.40 --- (3)
(3)
÷ 66 marbles + 6 stickers = 35.40
1 marble + 1 sticker = 35.40 ÷ 6
1 marble + 1 sticker = 5.90 --- (4)
(b)
(2) - (4)
(1 marble + 5 stickers) - (1 marble + 1 marble) = 15.50 - 5.90
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 = 5.90
1 marble + 2.40 = 5.90
1 marble = 5.90 - 2.40 = 3.50
Cost of 1 marble = $3.50
(d)
(4)
x 9 1 marble + 1 sticker = 5.90
9 x (1 marble + 1 marble) = 9 x 5.90
9 marbles + 9 stickers = 53.10
Cost of 9 marbles and 9 stickers = $53.10
Answer(s): (a) $5.90; (b) $2.40; (c) $3.50; (d) $53.10