the Visual-Text Art Venue
David Colosi
Exercise in Active Reading

Twelve balls exist. They are all of equal weight except for one which is either heavier or lighter than the others. Find the ball of different weight by weighing the balls only three times on a balance. Weigh four balls against four. If the scale is balanced eliminate all eight balls. Next weigh two of the remaining four balls against each other. If the scale is balanced then eliminate one of the balls on the scale and weigh one of the others against the ball on the scale. If the scale is balanced again then the ball that remained off the scale is Odd. If the scale is imbalanced then the most recent ball placed on the scale is Odd. If the scale is imbalanced after weighing two of the remaining four balls against each other then remove one and record it. Then weigh one of the remaining balls against the ball on the scale. If the scale is balanced then the ball that was removed is Odd. If the scale is imbalanced then the ball that initially remained on the scale is Odd. If the scale is imbalanced after weighing four balls against four balls then the Odd ball is on the scale. Replace three of the known Even balls (now off the scale) with three of the balls on the right side of the scale. Then take the three balls from the right side of the scale and replace them with three on the left side. Leave the three from the left side out. If the scale is imbalanced in the same direction then the odd ball is one or the other of the two balls that didn't change positions. Weigh one of those against a known Even ball to find the Odd one. If the scale is imbalanced in the opposite direction then you know that you've moved the Odd ball to the left side. You also know whether the Odd ball is heavy or light depending on how the scale changed. Weigh two of the possible Odd balls against each other, and if the scale is balanced then the Odd ball is the one not on the scale, but if it is imbalanced, the Odd ball is the one of the known weight difference. If the scale is balanced after the three ball rotation then the Odd ball is not on the scale. You also know whether the Odd ball is heavy or light from the orientation you found after initially weighing four balls against four. Again weigh two of the possible Odd balls against each other, and if the scale is balanced then the Odd ball is the one not on the scale, but if it is imbalanced, the Odd ball is the one of the known weight difference.