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Question: 2015 Fall Final - 15

Author: Michiel Smid
You are given that:
  • The course COMP 9999 runs over a period of one year, starting on January 1 and ending on December 31. There is one lecture every day; thus, the total number of lectures is 365.
  • Dania and Nick take this course. Dania's birthday is on November 19. Nick's birthday is on December 3.
  • Professor G. Ruesome teaches the course. Professor Ruesome decides to have 20 quizzes during the year. For this, he chooses a uniformly random subset of 20 days; the quizzes will be on the 20 chosen days. (It is possible that there is a quiz on January 1.)
Determine $\Pr(A)$, where $A$ is the event
  • A = "There is a quiz on Dania's birthday and there is a quiz on Nick's birthday".
(a)
$\left. {363 \choose 18} \middle/ {365 \choose 20} \right.$
(b)
$1 - \left. {363 \choose 20} \middle/ {365 \choose 20} \right.$
(c)
None of the above.
(d)
$\left. {365 \choose 18} \middle/ {365 \choose 20} \right.$