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Is this a trick question?

Savvy recruiters know that a potential employee's qualifications aren't the only measure of how well they'll fit into a company. They want insight into how a candidate thinks and tackles problems. With these brainteasers, it's not so much the answer that's important, but how the person arrived at it.

Why are manhole covers round? —Microsoft

This is an open-ended question with many possible answers. The most common "correct" answer is that a circle is the only shape where the cover could not fall into the hole if it was placed in diagonally. Other possible answers include: round holes are the easiest kind to dig, round covers are easier to move around because they can be rolled, and circular covers don't need to be carefully aligned to fit back in the hole.

You are shrunken to the size of a nickel and thrown into an empty glass blender. The blades start turning in 60 seconds. What do you do? —Google

OK, this one is a trick question. The idea is to see your thought process and gauge creativity. Do a search on Google (where else?) and you'll find entire message boards dedicated to dissecting this particular brain-teaser.

How do they make M&Ms? —Microsoft

It's unlikely that anyone other than a candy-trivia buff would know the answer to this, but the interesting part is to see if a candidate can grasp the potential complexity of making such a simple thing. The actual process is this: The chocolate centres are cast in molds, which are then placed in a rotating drum, where they're sprayed with liquid sugar. The sugar hardens into a shell. The constant movement keeps the candies from sticking together and also polishes them, like rocks in a rock tumbler. Printing the "M" on the candy is a whole other puzzle.

At 3:15, how many degrees separate the hands on a clock? —Goldman Sachs

This one is actually not that difficult to figure out—the correct answer just isn't the first one that occurs to you. At exactly 3:15, the hands on a clock are not aligned, because the hour hand has moved 15 minutes' worth of sweep away from the three. There are 48 15-minute segments in the motion of a 12-hour clock and 360 degrees in a circle. So the hour hand has moved 360/48, or 7.5 degrees.

Bonus question:

You have a five-gallon jug and a three-gallon jug. Measure out exactly four gallons

of water. —Smith Barney

Fill the five-gallon jug. Pour all but two gallons into the three-gallon jug. Empty the three-gallon jug. Put the two remaining gallons from the five-gallon jug into the three-gallon jug. Fill the five-gallon jug one more time. Pour one gallon from the five-gallon container by filling the three-gallon jug. Ta-da—now the five-gallon jug contains four gallons.