Newly prepared radioactive sample shows 4 times the allowed and safe value of radioactivity, so on reaching to the allowed and safe value, its radioactivity will be reduced to (
1
4
) th of the current value, ∵At=
A
(2)t/t1∕2
Here, A= current activity, At= final activity =
A
4
t= time-taken, t1/2= half-life =24h So, on putting the values