Question

The phone company NextFell has a monthly cellular plan where a customer pays a flat monthly fee and then a certain amount of money per minute used on the phone. If a customer uses 210 minutes, the monthly cost will be $108.5. If the customer uses 620 minutes, the monthly cost will be $252.

A) Find an equation in the form
y
=
m
x
+
b
,
where
x
is the number of monthly minutes used and
y
is the total monthly of the NextFell plan.

Answer:
y
=




B) Use your equation to find the total monthly cost if 979 minutes are used.

Answer: If 979 minutes are used, the total cost will be
dollars.
Get help: Video

Answer 1

1. y=0.35x+35

2. If 979 minutes are used, the total cost will be $377.65 dollars.

Explanation:

1. Let $x be the flat monthly fee and $y be the amount of money paid per minute used on the phone.

If a customer uses 210 minutes, the monthly cost will be $108.5, thus

`x+210y=108.5`

If the customer uses 620 minutes, the monthly cost will be $252, then

`x+620y=252`

Subtract from the second equation the first one:

`x+620y-(x+210y)=252-108.5\\ \\x+620y-x-210y=143.5\\ \\410y=143.5\\ \\y=0.35`

Substitute it into the first equation

`x+210\cdot 0.35=108.5\\ \\x=108.5-73.5\\ \\x=35`

We get the flat fee is $35 and the amount of money per minure used is $0.35. So, the equation of the function is

`y=35+0.35x,`

where x is the number of monthly minutes used and y is the total monthly of the NextFell plan.

2. When x=979, then

`y=35+0.35\cdot 979=377.65`