Two different radioactive isotopes decay to 10% of their respective original amounts. Isotope A does this in 33 days, while isotope B does this in 43 days. What is the approximate difference in the half-lives of the isotopes?

A. 3

B. 10

C. 13

D. 33

Let t = half-live

Isotope A:

0.1=2^ (-33/t)

take logs

log (0.1) = - (33/t) * log (2)

t=-log (0.1) log (2) / 33

=9.93 days

Isotope B:

0.1=2^ (-43/t)

take logs

log (0.1) = - (43/t) * log (2)

t=-log (0.1) log (2) / 43

=12.94 days

So work out the difference in half lives.