Question

The activity of a radioactive sample after 10 minutes is 1/5 of its original activity the mean life of radioactive substance in seconds

Answer 1

Law of radioactive decay:

$$N=N_0*2^{-t/T}$$

$$N_0/N=2^{t/T}$$

$$2^{t/(60*10)}=5$$ $$t=600*log_2(5)$$

Answer:

$$t=1393s$$

or 23m 13s