Answer:
2.2 % and 0 %
Explanation:
The equation we will be using to solve this question is:
N/Nâ  = eâ»Î» t
where  Nâ : Number of paricles at t= 0
      N=  Number of particles after time t
       λ= Radioactive decay constant
       e= EulerŽs constant
We are not given λ , but it can be determined from the half life with the equation:
λ = 0.693 / t 1/2 where t 1/2 is the half-life
Substituting our values:
λ = 0.693 / 55 s = 0.0126/s
a) For t = 5 min = 300 s
N / Nâ = e^-(0.0126/s x 300 s) = e^-3.8 = 0.022 = 2.2 %
b) For t = 1 hr = 3600 s
N / Nâ =  e^-(0.0126/s x 3600 s) = 2.9 x 10 â»ÂČâ° = 0 % (For all practical purposes)
