math
posted by lady .
The halflife of 234U, uranium234, is 2.52 105 yr. If 97.4% of the uranium in the original sample is present, what length of time (to the nearest thousand years) has elapsed?

2.52*10^5 = 252 thousand
do it all in thousands of years
.5 = e^k(252)
ln .5 = 252 k
solve for k
then
.974 = e^kt
ln .974 =  k t solve for t