Question 18
There are 100 metal balls which look exactly the same; 50 of them are radioactive. There are also three radiation detectors. For any group of balls, each detector is supposed to establish if there are radioactive balls in it or not. But it is known that one detector always gives the right answer, another one always gives the wrong answer, and the third one sometimes gives a right answer and sometimes a wrong one. However, it is not known which detector behaves in which way. Give a procedure by which the 50 radioactive balls can be sorted out with all certainty. The detectors can be used infinitely and with any amount of balls.