Question

The graph shows the amount of caffeine left in the body after drinking a 20-ounce soft drink with 90 milligrams of caffeine. Which of the following exponential equations best fits the data?

y=90(2)^
y=2(90)^x
y=0.5(90)^x
y=90(0.5)^x

Answer 1

y=90(0.5)^x

The y-intercept is (0,90), so when x=0, y should be 90.

By replacing x=0 in all equations you get;

1)

y=90(2)^0 =90 accepted

2)

y=2(90)^0 =2 rejected

3)

y=0.5(90)^0 =0.5 rejected

4)

y=90(0.5)^0 =90 accepted

Since this is an exponential decrease,

y=90(2)^x is rejected.