# Exponential Distribution and radio active decay

Half time = 1 year
λ = ln 2 here

Q 1: if we have 1024 atoms at t=0, what is the time at which the expected number remaining is one.

Easy, I get 10 years

Q 2: The chance that in fact none of the 1024 atoms remains after the time calculated in c:

it should be P(T<10 years) = 1 - P(T>10 years) but I get different answers.

any hints please? I know it's easy, I'm just missing something

Thanks