Solving a word problem using a system of linear equations of the form y = mx + b

Question

A phone company offers two monthly plans. Plan A costs $16 plus an additional $0.14 for each minute of calls. Plan B costs $26 plus an additional $0.09 for each minute of calls. For what amount of calling do the two plans cost the same? What is the cost when the two plans cost the same?

 

Answer 1

A=16+0.14m, B=26+0.09m are the plan equations where A and B are charges in dollars.

When A=B, 16+0.14m=26+0.09m, 0.05m=10, m=10/0.05=1000/5=200 minutes.

A=B=16+28=26+18=$44 is the cost.