[Judy]

Assuming that the half-life of a radioactive element is 5.2 years, how long does it take when this radioactive material decays to 2% of its original amount?
 
The answer is  B (see attachtment)

Here's my calculation:
log(2/100) / log(1/2) *5.2
None of the answer leads to this.

[Borek]

Not sure what the problem is, B and you answer seem to be equivalent.