Which Coin Did I Flip?

Level 2●●○○○ Easy~4 min

Problem

A bag has two coins: one fair (

P(H)=1/2

) and one double-headed (

P(H)=1

). You pick one uniformly at random, flip it, and see heads. (a) What is the probability you picked the double-headed coin? (b) If you flip the *same* coin again and get heads again, what is the updated probability?

←False Positives and Base Rates

4 / 36

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