Question

Two cell phone companies have different rate plans. Runfast has monthly charges $10 plus $4 per gig of data. B A &D’s monthly charge is $6 plus $6 per gig of data. Which company has the better deal for customers that don’t us much data? How do you know? Be sure to include how your response relates to the point of intersection.

Answer 1

BA&D's plan is better for those who use less data.  The intersection point of the two plans is (2, 18), which means that both plans cost $18 when you use 2G of data.  Anything using more data than that is less expensive with BA&D's plan.

To find the intersection point,
6+6g=10+4g

We cannot have a variable on both sides, so we will subtract 4g from both sides:
6+6g-4g=10+4g-4g
6+2g=10

Subtract 6 from both sides:
6+2g-6=10-6
2g=4

Divide both sides by 2:
2g/2 = 4/2
g = 2

This is the point where the plans cost the same.  If we try a number smaller than 2 in both plans,
6+6(1) = 6+6 = 12
10+4(1) = 10+4 = 14

BA&D's plan is less.