Originally Posted by
snippercr
You have 8 balls. All of them weigh the exact same, except for 1 which is JUST slightly lighter than the other.
You also have a traditional balance scale. Except, you are only allowed to use it to make 2 measurements. Can you determine which is the lighter ball?
(Friend was asked this on a business interview. Glad I am a pilot!)
Put 3 on each side of the scale -- if either side rises, you've narrowed it down to one of these three. Then put one of them on each side of the scale -- if one side rises, that's it, and if they balance, it's the third one. If, in the first weighing, the sides balanced, then just weigh the remaining two balls against each other.
The question could have specified 9 balls, but that might immediately suggest a 3/3/3 division, pointing you in the right direction too quickly.
