Remember this using this very old rhyme:-
Thirty days hath September,April, June, and November;All the rest have thirty-one,Save February, with twenty-eight days clear,And twenty-nine each leap year.
So January, March, May, July, August, October, and December have 31.
Seven
If by "only 31 days" you mean "exactly 31 days", then 7. If by "only 31 days" you mean "not more than 31 days" then all of them.
All 12 months have "at least" 28 days. Only February has exactly 28 days, except in leap year.
April, June, September, and November have 30 days, other months have 31 days, except February which has 28 days or 29 days in a leap year.
The probability is 7:12... There are five months with less than 31 days, so the probability of selecting a month with exactly 31 days is 7 out of 12.
30 days hath September, April, June and November. All the rest have 31 except for February.
11. The question is not specifically asking how many months have "exactly" 30 days. 11 months have "at least" 30 days. There are four months that do have exactly 30 days, and there are at least five different versions of this riddle.
Assuming there are 31 days in a month, it is nearly exactly one month,
It 31 days in this months
In a leap year, there are 186 days in the 31 day months and 180 days in the other months, so that is a difference of 6 days.
5 months don't have 31 days, 7 months do. February has 28, or 29 in leap years. April, June, September, and November have 30 days.
The common calendar presently in use worldwide has four different kinds of months. 187 days = 6.6786 months with 28 days each 187 days = 6.4483 months with 29 days each 187 days = 6.2333 months with 30 days each 187 days = 6.0323 months with 31 days each. (all rounded)