Posted by **Erica** on Tuesday, October 10, 2006 at 1:07pm.

The formula D= 5e ^-0.4h can be used to find the number of milligrams D of a certain drug that is in a patient's bloodstream h hours after the drug has been administered. When the number of milligrams reaches 2, the drug is to be administered again. WHat is the time between injections?

This looks more like algebra, where D equals 2. Solve for h and you'll have your answer in unit hours.

Solve the formula when D=2

2=5e ^-0.4h

Divide both sides by 5 and take the ln to solve for h.

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