1.
Let the sandwich be represented by = x
Let the drink be represented by = y
As given, Joe charges $10.00 for two sandwiches and one drink, so equation becomes 2x+y=10 ....(i)
He charges $6.50 for one sandwich and one drink, so equation becomes x+y=6.50 ....(ii)
Subtracting (ii) from (i) we get
x=3.50
And as x+y=6.50
y=6.50-3.50=3.00
Hence, cost of a sandwich is $3.50 and a drink is $3.00
2.
the question is incomplete. coordinates are missing
3.
Let x represent the number of performances
cost = 8000+300x
revenue = 700x
To break even, the cost must be equal to the revenue.
so x=20
Hence, 20 performances are needed to break even.
4.
Let us take x for 20% material, y for 50% material
......... (1)
Accounting for volumes to use, x+y=200 or x=200-y ................ (2)
Putting the value of x in (1)
y=66.67
x=200-y = 200-66.67 =133.33
Hence, 133.33 ml of 20% acetic acid and 66.67% of 50% acetic acid is needed.