There is a bucket containing 1000 coins.
1 of those coins has heads on both sides.
The other 999 are normal coins with heads and tails.
I pick one coin from random out of the bucket.
I flip this coin 10 times and receive heads every time.
What is the probability that the coin I picked was the coin with heads on both sides?
I know the answer works out to roughly a half but I don't know how to work it out... any help?