How Does Radioactive Decay Affect Isotope Ratios Over Time?

[Sublime74]

Homework Statement

A sample of radioactive isotopes contains two different nuclides, labeled A and B. Initially, the sample composition is 1:1, i.e., the same number of nuclei A as nuclei B. The half-life of A is 2 hours and, that of B, 4 hours. What is the expected ratio A/B after 8 hours?

Homework Equations

3. The attempt a solution

I know the number of nuclei decreases by a factor of 2 for each half life elapsed, but not sure how to go about this problem...

 

[glueball8]

Again Try N=No*(1/2)^t/T

No = original amount of radioactive material
N = amount of amount of radioactive material remaining after t
t = time intercal
T =half life

(1/2)^ta/Ta:(1/2)^tb/Tb