I thought of a red hammer. Nonetheless, I am suprised at the 98% statistic, and the replies so far don't justify it (although maybe most of us sheep are embaaarassed to own up)
It seems reasonable that "red" is the most commonly chosen colour (have a look at this http://www.righto.com/papers/laundry.ps - it still makes me laugh 10 years after I first saw it), and "hammer" the most commonly chosen tool, but even if they were each chosen 80% of the time, then, if the choices were independent, "red hammer" would only come up about 64% of the time.
I assume the arithmetic is intended to put one into a mind set of "give quick answer to easy question" rather than "think about what lies behind question and give a smart answer".