Finding the amount at the end of four hours

Question

One hundred milligrams of a drug are given to a patient. At the end of the hour the number of milligrams of the drug left in the body is 10% less than at the beginnig of the hour. How many milligrams of the drug are left in the body at the end of four hours?

Answer 1

Gee, after every hour, we have 90% of what was there before, since 10% is gone. To find the percent of something, we multiply.

 

100(.9)(.9)(.9)(.9) = 65.61 milligrams

 

Hope this helps!