finite math help please

Question

One of two urns is chosen at random with one as likely to be chosen as the other. Then a ball is withdrawn from the chosen urn. Urn 1 contains 1 white and 4 red​ balls, and urn 2 has 4 white and 1 red ball. If a white ball is​ drawn, what is the probability that it came from urn​ 2? Type as a fraction simplified the answer.

Answer 1

Use Bayes Theorem.

The probability of drawing a white ball from Urn 1 is 1/5. The probability of drawing a white ball from Urn 2 is 4/5. So this

(1/5) / [ (1/5) + (4/5) ] = 1 / [ 1 + 4 ]

= 1/5 that the white ball came from Urn 1.