There are twelve months in the year,
January, February, March, April, May, June, July, August, September, October, November and December
Nine of them have names that begin with a consonant,
January, February, March, May, June, July, September, November and December
Thus if you select a month at random there are nine chances in twelve that you will select a month that begins with a consonant. Hence the probability is 9/12 = 3/4.