Count Sandini calls himself the greatest "Sand Counter" in the world. Show him a bucket filled of sand, and in a few seconds he will tell you how many grains of sand are there!
Can you devise a (fairly quick) test to prove whether he can actually do so, or if he's a fraud?
After each test, either add or remove a little sand (don't forget
smoothing the sand so what you did isn't noticeable) and ask him if
there is more or less sand than before.
His odds are 50%-50%, so he has a 1 in 1,000,000 chance of getting it
right 20 times in a row. And, if you still suspect him, do the test 40
or 60 times...
A variation
