Put 3 balls in each pan,
if the scales are even, it's one of the two you have in your hands.
swap one of the two remaining balls with any ball on either scale.
if the scales are still even, it is the ball that hasn't been weighed yet,
it not, it is the ball you just placed on the scale.
other wise it is still on the scale.
Remove one ball from each pan and repeat until you have found your "odd ball"

Not sure, but you should find it in the given number of tries.

Ok, was in a bit of a hurry last night, Here is my revised answer. This will find your "odd ball" in 3 tries.


1. Put 2 balls in each pan
2.a. If scales are even, replace 2 balls in one pan with 2 unweighed balls.
3.a.1. If scales are still even, it is one of the 2 unweighed balls. Remove one ball from one side of the scale, and replace both balls from the other side with one unweighed ball. If they are even, it is the one ball that hasn't been weighed yet. If they are uneven, it is the ball you just placed on the scale.

2.b. If scales are uneven, remove one ball from each pan.
3.b.1. If the scales are even, it is one of the balls with one you just removed. Swap one of the balls that were removed from the scale with one of the balls on the scale. If the scales are uneven, it is the ball you just placed on the scale. If the scales are even it is the ball you did not place back on the scale.
3.b.2 If the scales are uneven, it is one of these two balls. Swap one of the balls that were removed from the scale with one of the balls on the scale. If the scales are still uneven, it is the ball that has been on the scale the whole time. If the scales are even, it is the ball you just removed from the scale.

Don't I get anything for getting it right? How about another one?