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1. The amount of a certain substance at time t (measured in seconds) is given by N(0.850t), where N is some constant. How long (in seconds) does it take until only 5% of the starting amount remains?

Can anyone help me with this question please?
2. (Original post by elef95)
The amount of a certain substance at time t (measured in seconds) is given by N(0.850t), where N is some constant. How long (in seconds) does it take until only 5% of the starting amount remains?

Can anyone help me with this question please?
Uh, surely the starting amount would be . Do you want to fix your question or post up a picture of it? (The latter would be very much welcome!)
3. (Original post by Zacken)
Uh, surely the starting amount would be . Do you want to fix your question or post up a picture of it? (The latter would be very much welcome!)
Could this be a Q where the stuff is used up and so the initial condition may be that the amount is non zero.

Post the question and all will be clear.
4. (Original post by nerak99)
This is a Q where the stuff is used up and so the initial condition may be that the amount is non zero.

Post the question and all will be clear.
Yes, that was my point.
5. (Original post by Zacken)
Uh, surely the starting amount would be . Do you want to fix your question or post up a picture of it? (The latter would be very much welcome!)
(Original post by nerak99)
Could this be a Q where the stuff is used up and so the initial condition may be that the amount is non zero.

Post the question and all will be clear.
Thanks for the replies! That's the whole question.
6. (Original post by Zacken)
Yes, that was my point.
Do you have any idea how to answer this question?
7. (Original post by elef95)
Do you have any idea how to answer this question?
As it is written, the question doesn't make sense. Could you provide a picture?
8. (Original post by elef95)
The amount of a certain substance at time t (measured in seconds) is given by N(0.850t), where N is some constant. How long (in seconds) does it take until only 5% of the starting amount remains?

Can anyone help me with this question please?
The amount increases with time, so the only possible solution is at 0.
9. I attached the image. Why can't the amount decrease over time?

(Original post by Zacken)
As it is written, the question doesn't make sense. Could you provide a picture?
(Original post by morgan8002)
The amount increases with time, so the only possible solution is at 0.
Attached Images

10. (Original post by elef95)
I attached the image. Why can't the amount decrease over time?
The question is not N(0.850t), as you said earlier.

Work out the initial amount. Then set the ratio of the amount at some later time to the initial amount to be 5%.
11. I'm sorry I wrote the question incorrectly! Do you know how to answer it now?

(Original post by Zacken)
As it is written, the question doesn't make sense. Could you provide a picture?
12. (Original post by elef95)
I'm sorry I wrote the question incorrectly! Do you know how to answer it now?
Initial amount is when and the initial amount is then . When there is only 5% remaining, we want to solve:

then use logarithms to solve this, can you take it from here?

PS: Can you now see the importance of attaching a picture or link of the question?
13. (Original post by Zacken)
Initial amount is when and the initial amount is then . When there is only 5% remaining, we want to solve:

then use logarithms to solve this, can you take it from here?

PS: Can you now see the importance of attaching a picture or link of the question?
Thank you! I got the answer Yes I can. I'll remember that for next time
14. (Original post by elef95)
Thank you! I got the answer Yes I can. I'll remember that for next time
Awesome. :-)

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