a basic cellular phone plan costs $18 per month for 50 calling minutes. Additional time costs $0.30 per minute. The formula C = 18+0.30 (x-50) gives the monthly cost for this plan for calling minutes, where x > 50. How many calling minutes are possible for a monthly cost of minimum $30 and a maximum $45?
30 <= 18+0.3(x-50) <= 45
12 <= .3(x-50) <= 27
40 <= x-50 <= 90
90 <= x <= 140
blah blah
To find the range of calling minutes for a monthly cost of minimum $30 and a maximum $45, we can use the given formula:
C = 18 + 0.30(x - 50)
First, let's solve the equation for the minimum cost of $30:
30 = 18 + 0.30(x - 50)
Subtract 18 from both sides:
12 = 0.30(x - 50)
Divide both sides by 0.30:
40 = x - 50
Add 50 to both sides:
x = 90
So, the minimum calling minutes for a monthly cost of $30 is 90 minutes.
Now, let's solve the equation for the maximum cost of $45:
45 = 18 + 0.30(x - 50)
Subtract 18 from both sides:
27 = 0.30(x - 50)
Divide both sides by 0.30:
90 = x - 50
Add 50 to both sides:
x = 140
So, the maximum calling minutes for a monthly cost of $45 is 140 minutes.
Therefore, the range of calling minutes for a monthly cost between $30 and $45 is 90 to 140 minutes.