[partygirluk]

You have 8 balls. You know that 7 of them weigh 500 grams. 1 of them weighs 499 or 501 grams. You do not know which is the odd one out.
All you have to help determine the black sheep is an old fashioned set of balancing scales, and three separate weighings.

Let the balls be A,B,C,D,E,F,G,H.

Outline a method which can guarantee identifying which ball weighs a different amount to the others AND whether it weighs more or less.