Brain Teaser #15 -

yes because it will be heavier than the others.

I tricked you. It can't be done with just one try. But it can be done if you use the scale twice. Weigh three coins with three other coins. If they're the same, then weigh the two remaining coins and the heavier one is the counterfeit. If one of the groups of three was heavier, weigh two of that group of three. If they're even, the third is the counterfeit. Otherwise, the heavier one is the counterfeit.