A probability value p is often reported as an odds ratio, which is p / (1 -

Question:

A probability value p is often reported as an odds ratio, which is p / (1 - p). This is the ratio of the probability that the event happens to the probability that the event does not happen.
(a) If the odds ratio is 1, what is p?
(b) If the odds ratio is 2, what is p?
(c) If p = 0.25, what is the odds ratio?