Question

What's 00.5 in a fraction?

Answer 1

1/2. it is one half because it is half of 1

Answer 2

I think you might have made a mistake writing your question, here are two possible answers, find out which one you need:
$0.05= \frac{5}{100} = \frac{1}{20}$
$0.5= \frac{50}{100} = \frac{1}{2}$