Suppose n students are each independently assigned a birthday in {1, ..., 365}, uniformly a random. Let Tn be the random variable equal to the number of unordered triples (i.e., sets of three distinct students) of students with the same birthday. (a) Show that if n > 120 then ETn 2 1. (b) How large must n be in order to guarantee that there are three students who share the same birthday, i.e. P(T, >1) = 1? %3D Find the least such n.

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Suppose n students are each independently assigned a birthday in {1, ... , 365}, uniformly at
random. Let Tn be the random variable equal to the number of unordered triples (i.e., sets of
three distinct students) of students with the same birthday.
(a) Show that if n > 120 then ET, 2 1.
(b) How large must n be in order to guarantee that there are three students who share the
same birthday, i.e.
P(T, > 1) = 1?
Find the least such n.
Transcribed Image Text:Suppose n students are each independently assigned a birthday in {1, ... , 365}, uniformly at random. Let Tn be the random variable equal to the number of unordered triples (i.e., sets of three distinct students) of students with the same birthday. (a) Show that if n > 120 then ET, 2 1. (b) How large must n be in order to guarantee that there are three students who share the same birthday, i.e. P(T, > 1) = 1? Find the least such n.
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