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Question: 2015 Winter Final - 17

Author: Michiel Smid
Consider a uniformly random bitstring of length 5. Define the events
  • A = "the bitstring contains exactly two 0s",
  • B = "the bitstring contains an even number of 0s".
(Note that zero is even.) What is the conditional probability $\Pr(A|B)$?
(a)
$\left. 2^5 \middle/ {5 \choose 2} \right.$
(b)
$\left. {5 \choose 2} \middle/ 2^3 \right.$
(c)
$\left. {5 \choose 2} \middle/ 2^5 \right.$
(d)
$\left. {5 \choose 2} \middle/ 2^4 \right.$