How do I work out parent/daughter isotope ratio?

i have a question similar to this:


If a radioactive parent isotope decays to produce a stable daughter isotope, what will be the daughter to parent ratio (D/P) after (.....) half-lives? You should give your answer as a single number.





how do i express a ratio as a single number?? i thought they were always in form, a:b.


is there a way to work this out???


can anybody help?How do I work out parent/daughter isotope ratio?
After one half-life has elapsed, half the parent has turned to daughter so the D/P is a half.