Problem

Two identical samples (same material and same amount)

P

and

Q

of a radioactive substance having mean life

T

are observed to have activities

A_P

and

A_Q

respectively at the time of observation. If

P

is older than

Q

, then the difference in their age is a.

T \ln \left( \frac{A_P}{A_Q} \right)

T \ln \left( \frac{A_Q}{A_P} \right)

T \left( \frac{A_P}{A_Q} \right)

T \left( \frac{A_Q}{A_P} \right)