a brain teaser

you send them to the coop board... and see which one gets rejected faster.

3 3 and 3, take two pairs of three and weigh them. if they balance, the heavy ball is in the third group of 3. then take the third group of three and weigh two of the three, if one is the heavy one, you'll know. and if the scales balance you know the other is the heavy one. if on the first weighing, one of the two sides is heavier, take those three and do the same second weighing routine.

scoop of chocolate, scoop of vanilla

How many different weights, in ounces, can be measured using only 4 counterweights and a balance? Try this

This one is pretty easy for you know the ball is heavier.

Let's say you have 12 balls and one is different, but you don't know if it is lighter or heavier. How would you identify it if you could use a pair of balance scales only three times?

Its the same problem stated differently-you can always identify the odd ball out
in three weighings

job interview question?

No - co-op interview question