>>Evan,
>>
>>>Here's a fun one. http://www.boingboing.net/2005/08/24/puzzle_of_the_month_.html
>>
>>This is the entire universe of possibilities (assuming integer ages)
>>
>>

>>a      1       1     225
>>b      1       3      75
>>c      1       5      45
>>d      1       9      25
>>e      1      15      15
>>f      3       3      25
>>g      3       5      15
>>h      5       5       9
>>

>>
>>a can be eliminated because 225 is an impossible age to attain. e g and h can be eliminated because the oldest person is not of legal age to own a home. f could be eliminated because it sums to the same value as e. But I don't see any way to eliminate down to only one of the remaining b, c and d candidate solutions.
>
>They key to moving further ahead is that the cenus taker must ask another question to determine the ages. He already knows the house number (the sum), so he should be able to get the ages, but he can't.

I don't see it. If the house number is 31 and he's trying to decide between the two that add to 31 the answer to the oldest person question is irrelevant, any one of the three people can have answered the door.