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(ex 13) (probability) If a certain coin is flipped, each of

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by Max@Math Revolution » Mon Sep 26, 2016 4:46 am
(ex 13) (probability) If a certain coin is flipped, each of the probabilities that the coin will land heads or tails is 1/2. If the coin is flipped 4 times, what is the probability that it will land twice tails up on the 4 flips?
A. 3/8 B. 1/16 C. 1/2 D. 5/8 E. 11/16
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by Max@Math Revolution » Wed Sep 28, 2016 3:16 am
==> Just like HHTT, out of 4 flips, the chances of getting 2 heads and 2 tails is 6 (4!/2!2!=6) in HHTT. If so, the chances of getting HHTT is (1/2)(1/2)(1/2)(1/2)=1/16, and 1/16*6=3/8. Therefore the answer is A.
Answer: A
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