There are four balls in a hat: a blue one, a white one, and two red ones. Now I draw simultaneously two balls, look at them, and announce that at least one of them is red.
What is the chance that the other is red as well?
If you need at least one of them to be red, you may as well look in the hat and pull out a red one. (Simultaneity doesn't really matter either.) Then randomly choose the other. The chance it is red is 1/3.

Posted by Jer
on 20170519 11:56:13 