I love these weighing puzzles and have long been my favourites. Does anyone know the origins of this one? -

I have six snooker balls. One set consists of a red, blue and white weighing 1kg each. The second set consists of a red, blue and white weighing 2kg each.
Determine which balls weigh which in only two weighings on a balancing scale.

Number the balls R1, R2, B1, B2, W1, W2

First weighing: R1 and B1 vs R2 and W1
Second weighing: B1 vs W2

There are 9 possible outcomes but only 8 possible weights - so it is solveable.

R1, B1 heavy and B1 heavy: R1=2, R2=1, B1=2, B2=1, W1=2, W2=1
R1, B1 heavy and B1 equal: R1=2, R2=1, B1=1, B2=2, W1=2, W2=1
R1, B1 heavy and B1 light: R1=2, R2=1, B1=1, B2=2, W1=1, W2=2

etc.