Question

Curt just drank a cup of coffee to help him stay awake. The coffee had 130 milligrams of caffeine in it. If his body processes 7% of the caffeine every hour, how much will be left in 4 hours?

93
94
98
91

Answer 1

Since we have to multiply it by 0.07 4 times (for each hour), we have 130 * 7^4

Answer 2

After 4 hours, there will 91.31 miligrams of caffeine within his body.

Explanation:

Givens

• Curt drank 130 miligrams of caffeine.
• His body processes 7% of caffeine everyhour.

If Curt's body processes 7% every hour, we just need to that 7% after each hour. Also, we know that 7% equals 0.07.

First hour.

`0.07(130)=9.1ml`

The first hour, his body processed 9.1 miligrams, so it remains

`130-9.1=120.9ml`

There's still 120.9 miligrams in his body.

Second hour.

`0.07(120.9)=8.46ml`

`120.9-8.46=112.44ml`

Third hour.

`0.07(112.44)=7.87ml`

`112.44-7.81=104.63ml`

Fourth hout.

`0.07(104.63)=7.32ml`

`104.63-7.32=97.31ml`

Therefore, after 4 hours, there will 91.31 miligrams of caffeine within his body.