The description says you have five minutes to complete the task. So just move any ten coins to a new pile. Continue moving one coin at a time while asking if

The description says you have five minutes to complete the task. So just move any ten coins to a new pile. Continue moving one coin at a time while asking if you have completed the task. You will have to move at most eighty coins after the initial ten. Since you have five minutes to do this, you'll have about 3-4 seconds per coin for the captor to reply if you've solved it yet. The solution someone posted to flip each coin after picking out twenty is faster but flawed; it would be too easy for a nervous and blinded person to flip the same coin twice. The best solution would be to flip each coin as it's drawn from the initial set of one hundred.