Statistics/Probability
posted by Heidi on .
The probability the New Year's day is on Saturday is a randomly chosen year is 1/7.
15 years was chosen randomly. Find the probability that,
(1) Exactly four of these years have a New Year's day on a Saturday.
(2) At least two of these years have New Year's day on a Saturday.

prob(Saturday) = 1/7
prob(not Saturday) = 6/7
prob(exactly 4 of 15 years is a Saturday)
= C(15,4) (1/7)^4 (6/7)^11
= appr .1043
at least 2 Saturdays > 1  (case of 0 Saturday + case of 1 Saturday)
= 1  (6/7)^15  C(15,1)(1/7)(6/7)^14
= .6534
check my arithmetic