Question

a month of the year is chosen at random. What is the probability that it has 31 days

Answer 1

There are 12 months, 7/12 have 31 days. You would have a 7/12 probability of choosing one with 31 days if it is random.

Answer 2

How many months of the year have 31 days?  Jan, Mar, May, Jul, Aug, Oct, Dec.  That's 7 months out of 12.  Thus, if you were to pick a month from these 12, the chances that you'd pick one that had 31 days would be 7/12, or approx. 0.58.