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?

Thanks