Results 1 to 7 of 7

- February 25th 2010, 10:35 AM #1

- Joined
- Feb 2010
- Posts
- 8

## help with a question

the active chemical in a certain medicine breaks down according to an exponential law. if the chemical has a half life of 20 years find the shelf life of the medicine if it is considered to be expired when less than 90% of the active chemical is still available...

pls can someone show me how to go about these type of questions as i have many similar questions to go through like this...

- February 25th 2010, 10:46 AM #2

- February 25th 2010, 10:56 AM #3

- Joined
- Feb 2010
- Posts
- 8

- February 25th 2010, 11:12 AM #4

- Joined
- Feb 2010
- Posts
- 38

you use the 1/2 as your base because its a half life, and then it is to the x power, but since the half life only occurs every 20 years the x is over 20.

Now to find when there is less than 90% of the chemical you simply set the equation equal to .1, aka 10%, and solve.

- February 25th 2010, 11:20 AM #5

- February 25th 2010, 12:10 PM #6

- Joined
- Feb 2010
- Posts
- 8

hi there thanks for the help with that question....are these the type of questions that logs are needed for?? bcuz i got a question like in 1990 west germany population was 60 million and decreasing at rate of 0.1% per year, and east germany population was 16 million and increasing at 0.06% per yr...if this continued when would the populations be equal? my friend tells me the answer is definately 2816AD but he uses a really complex formuale. is it possible to work this out with logs as they seem really handy. thank you

- February 25th 2010, 11:25 PM #7

- Joined
- Feb 2010
- Posts
- 38

hi there thanks for the help with that question....are these the type of questions that logs are needed for?? bcuz i got a question like in 1990 west germany population was 60 million and decreasing at rate of 0.1% per year, and east germany population was 16 million and increasing at 0.06% per yr...if this continued when would the populations be equal? my friend tells me the answer is definately 2816AD but he uses a really complex formuale. is it possible to work this out with logs as they seem really handy. thank you