Use Bayes Theorem to compute that probability. I will denote bath as [tex]B[/tex] and nap as [tex]N[/tex], the probability will be denoted as [tex]P(B)[/tex] or [tex]P(N)[/tex].
By Bayes Theorem
[tex]P(B\mid N)=\frac{P(N\mid B)\cdot P(B)}{P(N)}[/tex]
Which reads,
"What is the probability of [tex]B[/tex] given [tex]N[/tex]".
We know that [tex]P(N\mid B)[/tex] is 1 because we already took a bath. So the formula simplifies to,
[tex]P(B\mid N)=\frac{P(B)}{P(N)}[/tex]
Now insert the data,
[tex]P(B\mid N)=\frac{1/5}{4/5}=\boxed{\frac{1}{4}}[/tex]
So the probability that you will take a bath is [tex]0.25[/tex] after you have taken a nap.
Hope this helps. :)
