Answer:the cost of one roll of streamer is $2.5
the cost of one hat is $1.5
Explanation:
Let x represent the cost of one roll of streamer.
Let y represent the cost of one hat.
Suppose you bought supplies for a party. Three rolls of streamers and 15 party hats cost $30. This means that
3x + 15y = 30 - - - - - - 1
Later you bought 2 rolls of streamers and 4 party hats for $11. This means that
2x + 4y = 11 - - - - - - - -2
We will use method of elimination to solve both equations
Multiply equation 1 by 2 and multiply equation 2 by 3. It becomes
6x + 30y = 60
6x + 12y = 33
Subtracting to eliminate x,
18y = 27
y = 27/18 = 1.5
Substituting y = 1.5 into equation 1, it becomes
3x + 15×1.5 = 30
3x + 22.5 = 30
3x = 30 - 22.5 = 7.5
x = 7.5/3 = 2.5