Which equation best describes the pattern in the table below?
minutes cost
20 $10.00
40 $20.00
60 $30.00
80 $40.00

First find the slope, (y2-y1)/(x2-x1)=(20-10)/(40-20)=10/20=1/2

y=mx+b, where m is the slope and b is the y-intercept

y=x/2+b, using any point we can solve for b, I'll use (20, 10)

10=20/2+b

10=10+b

0=b, so the cost function is:

C(m)=m/2  (cost in dollars as a function of minutes is minutes divided by two)