At how many lines is the monthly cost the same? What is the monthly cost of the two plans?

Question

Penny is looking at two phone plan options. Buzz Mobile's monthly charges are $53.99 for data and $19.99 per line. Quick Call's monthly charges are $35.99 for data and $25.99 per line.

Answer 1

Hi Elizabeth,

 

Cost equations as a function of number of lines:

 

Buzz:  C(L) = 53.99 + 19.99L

Quick:  C(L) = 35.99 + 25.99L

 

To find how many lines makes the cost the same

set the equations equal and solve for L

 

35.99 + 25.99L = 53.99 + 19.99L

Sbtract 19.99L from both sides

35.99 + 6L = 53.99

Subtract 35.99 from both sides

6L = 18

L = 3

 

The costs are the same for 3 lines.

 

To find the equal cost at 3 lines, just put 3 in

for L in the original cost equations to find the

monthly charge.

 

Understand?