Flip 98 fair coins and 1 HH coin and 1 TT coin. Given that you see an H, what is the probability that it was the HH coin? Explain in layman’s terms.

Fair coins: Head (H) and Tail(T)
HH coin: Both sides are head
TT coin; Both sides are tail

Answer below:

  • There are 100 heads in total.
  • 2 of those heads come from the HH coin
  • The probability is therefore \frac{2}{100}

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