Question

A cup of coffee has approximately 310 mg of caffeine. Each hour, the caffeine in your system decreases by about 35%. How much caffeine would be left in your system after 5 hours? Round to the nearest whole.

Answer 1

36 mg

Explanation:

Please refer to the attached image for explanations

Answer 2

Amount of caffeine left after 5 hours = 36 mg

Explanation:

We are told that the cup has 310 mg of caffeine originally.

Since it decreases by 35 percent or 0.35 each hour, it means that for each additional hour, the new amount of caffeine would be (1 - 0.35) x previous amount i.e. 0.65 x previous amount. Thus;

After 0 hour, we have; 310 mg

After 1 hour, we have; 310(0.65)

After 2 hours, we have; 310(0.65)(0.65)

After 3 hours, we have; 310(0.65)(0.65)(0.65)

We can see this follows a pattern of;

A(t) = 310(0.65)^(t)

Where;

A(t) is the amount left after t hours

And t is time t hours

Thus, amount left after 5 hours is;

A(5) = 310(0.65)^(5)

A(5) = 310 x 0.11603

A(5) ≈ 36 mg