13. Among 9 randomly selected students, the probability that at least 2 students are born in the same month is $\_\_\_\_$ (assuming each month has the same number of days; round the result to 0.001)
13. Among 9 randomly selected students, the probability that at least 2 students are born in the same month is $\_\_\_\_$ (assuming each month has the same number of days; round the result to 0.001)