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# Yet another C3 quetion watch

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1. So this is the question

http://www.mei.org.uk/files/papers/c305ju_dskjtr.pdf
Question 4 on the rate of change.

Everything is fine until it comes to substtituting t=40 into the equation, the mark scheme has " e^-0.05t= 1/2 " on the second line
Could someone please explain where the 1/2 came from, i have no clue whatsoever. Thanks allot
2. put in T=40, then take away the 30 to get 10 divide by 20 to get 1/2, then take lns..... i think????
3. (Original post by jenny28)
put in T=40, then take away the 30 to get 10 divide by 20 to get 1/2, then take lns..... i think????

that's what i got

40 = 30+20 e^-0.05t
40-30 = 20e^-0.05t
10 = 20e^-0.05t
10/20 = e^-0.05t
1/2 = e^-0.05t
4. Thank-you sooo much, I just couldn't see it at all. I swear sometimes m/s are more confusing than helpfull!

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Updated: January 19, 2010
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