Your question is Double-Sided Coin Probability. Take a moment with it on the right.
Talk me through your thinking if you like. When you're confident, submit your answer and I'll grade it like a real screen (7/10 or better passes).
You have 1000 coins, 999 of which are fair and the other 1 remaining is heads on both sides. You pick a coin at random, flip it 10 times, and get 10 heads in a row. What is the probability it is the double head-sided coin?