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Solution: 2015 Fall Midterm - 15

Author: Michiel Smid

Question

You flip a fair coin 7 times. Define the event
  • A = "the result of the first flip is equal to the result of the 7-th flip".
What is $\Pr(A)$?
(a)
$\frac{2^5 + 2}{2^7}$
(b)
$1/4$
(c)
$1/2$
(d)
$1/3$

Solution

There are 4 possible total outcomes for the first and last flip:

  • HH
  • HT
  • TH
  • TT

|A| = 2

$Pr(A) = \frac{2}{4} = \frac{1}{2}$