The half-life of 234U, uranium-234, is 2.52 105 yr. If 98.6% of the uranium in the original sample is present, what length of time (to the nearest thousand years) has elapsed?
.986=e^(-.693t/2.52E5)
take the ln of both sides..
> -0.0140989244=-.693t/2.52E5
solve for t
t== 0.693147181*2.52E5/0.0140989244
I get a little over 12 million yars