A sample is dated using uranium-235 (half-life 704,000,000 years) and it has 4 of the original amount of uranium. How old is the sample?

May 3, 2017

$1 , 408 , 000 , 000$ or $1.408 \cdot {10}^{9}$ years

Explanation:

note: it is impossible to have a value higher than 1 times the original amount if the sample is dated back, so i'm going to assume that you meant $\frac{1}{4}$.

using this:

$\frac{1}{4} = \frac{1}{2} \cdot 2$

meaning $2$ half-lives have passed.

$2$ * half-life of uranium $= 2 \cdot 704 , 000 , 000$

$= 1 , 408 , 000 , 000$ years or $1.408 \cdot {10}^{9}$ years, in standard form.