Question

A phone company 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 410 minutes, the monthly cost will be $71.50. If the customer uses 720 minutes, the monthly cost will be $118. Find a linear equation for the monthly cost of the cell plan as a function of x, the number of monthly minutes used.

Answer 1

Answer:

Linear equation for the monthly cost of the cell plan is $10+0.15x$

Step-by-step explanation:

Let u denotes a flat monthly fee and v denotes amount charged per minute.

As the monthly cost is $71.50 if a customer uses 410 minutes,

$71.50=u+410v$     (i)

As the monthly cost is $118 if a customer uses 720 minutes,

$118=u+720v$       (ii)

Subtract (i) from (ii)

$118-71.50=u+720v-u-410v\\46.5=310v\\v=\frac{46.5}{310}\\ v=0.15$

Put $v=0.15$ in (i)

$71.50=u+410(0.15)\\71.50=u+61.5\\u=71.50-61.5\\u=10$

As x denotes the number of monthly minutes used,

linear equation for the monthly cost of the cell plan is $10+0.15x$