Question

The Half-Life of Pa-234 is 6.75 hours. How much (what fraction) of a sample of this isotope remains after 20.25 hours?

Answer 1

So in one hour half the amount remains (that's what half life means). In two hours 1/4 (or half of half) would remain and in three hours 1/8 would remain.
So the answer is 1/8