What you can do is use the formula
Nt = N0 [(1 / 2) ^ (t / t(1/2) )
where
Nt = current amount of radioactive substances.
N0 = Initial amount of radioactive substances.
t1/2 = half life of radioactive substances.
t = quantity of substances remains after the time t.
Related to what we have, we use the data like this:
Nt = 200 mg, N0 = 250 mg, , t = 48 hours
Then
200 = 250 [ (1/2)^ (48 / t(1/2) ) ]
(1/2)^ (48 / t(1/2) ) = 200/250 = 0.8
48 / t(1/2) = Log ( with the base of 1/2 ) 0.8 = log 0.8 / log 0.5 = 0.32
t(1/2) = 48 /0.32 = 150
I hope this can help you a lot
