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/sci/ - Science & Math

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1886541 No.1886541 [Reply] [Original]

Just had a math test, this problem i had has been bugging the shit out of me because I'm pretty sure I did it wrong. can /sci/ help?

It was the exponential decay of carbon-x on a bull, when the half-life is 5,726 years. right now the dead bull only has 25% of it left. using Pe^rt, I set it up like this:
(1/2)=(1/4)e^r5,726. (1/4) representing 25% and 1/2 representing halflife.
so that comes down to ln((1/2)/(1/4))/5726 which =a rate of 0.000121.
so then I got ln(1/4)/0.000121=t
t=11457.

is this right?

>> No.1886557

dat picture

>> No.1886558

Did you get a gud grade?

>> No.1886565

Not graded yet, just can't stop thinking about it. College Midterm.

>> No.1886580

anyone?

>> No.1886597
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1886597

>> No.1886598

>>1886541

Correct answer, but you could have just multiplied the time by 2.
50% = 1 half life = 5,726 yrs
25% = 2 half lives = 2*5726 = 11452 yrs
12.5% =3 half lives= 3*5726 = 17178 yrs
and so on.

>> No.1886602

Sweet, thanks

>> No.1886603

You don't even need the formula. If 25% of it has left then it has undergone 2 half lives or 5,726 x 2. ( I got 11452)