Question

The phone company Splint has a monthly plan where a customer pays a flat monthly fee, and then a set rate per minute. If a customer uses 130 minutes, the monthly cost will be $57. If the customer uses 520 minutes, the monthly cost will be $135.

Find the equation of the plan in the form y=mx+b, where x is the number of monthly minutes used and y is the total monthly cost of the Splint plan.

y= _______________

If a customer uses 855 minutes, the total cost will be ____________ dollars.

Answer 1

y = 0.2x + 31

855 minutes would cost $202.

Explanation:

Let,

a be the cost per minute and f be the flat fee charged.

Now,

130a + f = 57 Eqn 1

520a + f = 135 Eqn 2

Subtracting Eqn 1 from Eqn 2

520a + f - 130a - f = 135 - 57

390a = 78

Dividing both sides by 390

a = $0.2

Putting in Eqn 1

130 (0.2) + f = 57

26 + f = 57

f = 57 - 26

f = 31

Hence the company charges a flat fee of $31 and $0.2 per minute.

Equation in slope intercept form.

y = 0.2x + 31

Now putting x = 855

y = 0.2(855) + 31

y = 171 + 31

y = $202

Therefore,

y = 0.2x + 31

855 minutes would cost $202.