What’s the probability that 3 people are born in September?

Answer 1

Mike has a 1/12 probability of birth in September.

Jay has a 1/12 probability of birth in September.

Cathy has a 1/12 probability of birth in September.

Probability of all three being born in September would be

1/12 (1 month of September out of 12 months in a year) ×

1/12 × 1/12 or 1 out of 1728 or 0.000578703703 equivalent

to 0.000579 (579 chances in 1000000).

With 30 days in September, one might also write

30/365 (30 September days out of 365 days in a year)

× 30/365 × 30/365 or (6/73)³ or 216/389017

or 0.0005552456576 equivalent to 0.000555

(555 chances in 1000000).