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counting and probability intermediate

Problem

What is the positive difference between the probability of a fair coin landing heads up exactly 2 times out of 3 flips and the probability of a fair coin landing heads up 3 times out of 3 flips? Express your answer as a common fraction.
Solution
The probability that a fair coin lands heads up exactly 2 times out of 3 flips is . The probability that a fair coin lands heads up 3 times out of 3 flips is . Finally, we have .
Final answer
\frac{1}{4}