A Census-taker stopped at a lady's house and wanted to find out
how many children she had. The lady, a math teacher, wanted to
see if the Census-taker still knew his math.
Census-taker to lady: How many children do you have?
Lady: Three.
Census-taker: How old are they?
Lady: the product of their ages is 36.
Census-taker: Well, that's just not enough information.
Lady: The sum of their ages is our house number.
Census-taker looks at the house number thinking this would give it
away, but says: Still not enough information!.
Lady: My oldest child plays the piano.
Census-taker: AHA! I know now. Thank you!