The table is:
Number of washes denoted by x: 0, 8, 12
Amount left on card denoted by y: 30, 18, 12
a. Write an equation that shows the amount of dollars left on the card
Solution:
18 – 30 divided by 8 – 0 = -12/8
On simplest form is -3/2
The equation is y = -3/2x + 30
b. Explain the meaning of the negative slope above.
As the number of car washes increase, the dollars left on the card decreases.
c. What is the maximum value of x?
0 = -3/2x + 30
2/3 x 3/2 x = 30/1 x 2/3
Cancel 2/3 x 3/2 and reduce 30 by 3 we get 10, 10 x 2
x = 20