Welcome to your interview.
The question is on your right: Double-Sided Coin Probability. Take a moment with it first.
Talk your thinking through with me if you like - when you're confident, submit your answer and I'll grade it like a real screen (7/10 or better passes). Discussion and graded submissions share your five interviewer interactions, so spend them well.
You have a bag of coins where one coin is double-sided (heads on both sides) and the rest are fair. You pick a coin at random and flip it three times; it lands on heads each time. What is the probability that you chose the double-sided coin?