The nuclei of two radioactive isotopes of same substance `A^(236)` and `B^(234)` are present in the ratio of `4:1` in an ore obtained form some other planet. Their half-lives are 30 and 60 minutes respectibvely. Both isotopes are alpha emitters and acitity of isotope `A^(236)` si 1 rutherford `(10^(6) dps)`. Calcualte:
(a) After how much time their activities will becomes identical?
(b) The time required to bring the ratio of their atoms to `1:1`
