How do you calculate the number of days required for 3/4 of a given amount of nuclide to decay if the half-life is 18 point 72 days?
You calculate the number of half-lives and multiply by the length of one half-life.
The number of half-lives is
For each half-life, you divide the total amount of the isotope by 2, so
Amount remaining =
You can rearrange this to
If original amount was 1, and