The half-life of 234U, uranium-234, is 2.52 multiplied by 105 yr. If 98.7% of the uranium in the original sample is present, what length of time (to the nearest thousand years) has elapsed?

yr

From an article on 234U, I find that the half-life is 245,500 years. What do you mean by "2.52 multiplied by 105 yr"?

Your earthquake question also had a weird measurement: "5.28 multiplied by 102µ" or some such.

Eh?

Anyway, using my figure of 245,500 yr, the formula for the amount of 234U is

A(t) = A02-t/245500

You can see that at t=245500, A = A02-1, or 1/2 the initial amount.

So, plug in .987 for your fraction, and see what t comes out to be.