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Temperature problem

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Master | Next Rank: 500 Posts
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by The Jock » Wed Oct 08, 2008 5:46 am
the temperature of a certain cup of coffee 10 minutes after it was poured was 120 degrees fahrenheit. if the temperature f of the coffee t minutes after it was poured can be determined by the formula f=120(2^-at) + 60, where f is in degrees fahrenheit and a is a constant, then the temperature of the coffee 30 minutes after it was poured was how many degrees faherenheit?
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by ab78 » Sat Oct 11, 2008 11:53 am
The temp f=120(2^-at) + 60

after 10 mins given temp is 120, substituting

120-60 = 120(2^-a10)

1/2=2^-10a

10a=1 therefore a= 1/10

now substitute after 30 mins f = 120(2^-3) + 60 = 75

wat is the answer?
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by jnellaz » Fri Nov 07, 2008 6:33 am
Hey ab78 -

Can you explain how you got from

1/2=2^-10a

to

10a=1?

I lost you on that.
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by jimmiejaz » Fri Nov 07, 2008 7:39 am
jnellaz wrote:Hey ab78 -

Can you explain how you got from

1/2=2^-10a

to

10a=1?

I lost you on that.
1/2 = 2^-1.
comparing both sides we get,
-1=-10a
a=1/10

hope u r clear now.
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by stickyfingers48 » Sat Nov 08, 2008 7:01 am
Hey ab78 -

Can you explain how you got from

1/2=2^-10a

to

10a=1?

I lost you on that.


Substitute this value of a in the following equation:

F= 120*(2^-10/a) +60

The answer is 75
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