The IRS says it will audit about 20 percent of all tax returns next year. What are the odds in favor of your being audited?

I cant find the formula that I would need for this problem, how can I solve it without knowing how many tax returns there are?

Thanks for your help

You've already been given the probability, which is 0.20, so you just need to convert the probability into odds.

Let A be the event that a return is audited.
Given P(A) = 0.20
Then A' is the event that a return isn't audited.
P(A') = 1 - P(A) = 1 - .20 = .80

Odds in favor = P(A) / P(A')
= .2/.8 = 1/4

Odds in favor = 1:4