Question

If there is a radiation that has a half life of 10 days and we have it for 110 days, what will be the fraction of radiation left?

Answer 1

k = 0.693/t_1/2

Solve for k and substitute into the equation below.

ln(No/N) = kt.
No = atoms to start.
N = atoms left
k from above.
t = time.
There is no No to start; the problem asks for the fraction left or N/No; therefore, you want to solve for No/N and take the reciprocal.