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A team of archaeologists recovered wooden artifacts believed to be 4000 years old. How much carbon-14 has been lost from the wood?
the decay rate for carbon -14 is 0.00012 
I can't figure out how to put this in A formula.... Any help is appreciated! 
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2 Answers

Dear Erica,
In general
A = A0e-kt
where A is the amount remaining after t years, A0 is the starting amount and k is the decay constant.
Let us rewrite this as
A/A0 = e-kt = e-[(0.00012)*(4000)] = e-0.48 = 0.62
I think all we can say with certainty is that, during those 4000 years, the amount of C-14 decreased to 62% of its original value, or it lost 38% of its original value (A0).
N(t)=N(0)e-kt, where k is the decay rate. I assume k=-0.00012 is measured in year-1, so that t is in years (in fact, it is the case, I believe, since half-life time is 5730 years for C14).
So the amount of carbon-14 left at the present moment is 0.62 or 62% of its original quantity. Therefore, 38% has been lost due to decay.
Answer: 38%