Suppose there are 10 coins laid out in front of you. All of the coins are fair except one, which flips to heads every time. You draw one coin at random and flip it 5 times. If each of the 5 flips results in heads, then the probability that this coin is fair can be written as a/b, where a and b are coprime positive integers. What is the value of a+b?

Is it 19?

Question

Suppose there are 10 coins laid out in front of you. All of the coins are fair except one, which flips to heads every time. You draw one coin at random and flip it 5 times. If each of the 5 flips results in heads, then the probability that this coin is fair can be written as a/b, where a and b are coprime positive integers. What is the value of a+b?

Is it 19?

anonymous · Answer

How did you set this one up? Let me try to draw it if I didn't get any misconceptions:

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