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hen logic flawed?

For this question:
"if a hen and a half lay an egg and a half in a day and a half, how many hens does it take to lay six eggs in six days? "

The answer posted is:
"if 1.5 hens lay 1.5 eggs in 1.5 days (or 36 hours) then: 1 hen lays 1 egg in 1,5 days or 4 eggs in six days thus 1.5 hens lay 6 eggs in 6 days"

This answer adds the assumption that a single hen will produce two thirds as much as 1.5 hens in the same amount of time. Where did that assumption come from? And why assume  the same amount of time? Why not assume that a single hen produces a single egg in a single day, unencumbered by the extra half a hen? Or that it takes 2 full days without the assistance of the extra half hen?

Notice also that the question asks about producing six eggs, not half eggs. No marvels of egg-grafting technologies are mentioned, so we can't assume that the half egg produced during a 1.5 day shift counts for anything.

Sticking with just the given facts, wouldn't 1.5 hens produce 4 eggs and 4 half-eggs in 6 days?  Clearly this is insufficient. Not knowing what an additional single hen or half hen can produce, we need to hire another 1.5 hens.

Assuming they haven't unionized by now, we can make our 2 1.5 hen teams work 4 consecutive 1.5 day shifts (6 days), producing a total of 8 eggs and 8 half-eggs, overshooting our target by 2 eggs and 8 half-eggs.

It seems to me that with the conditions set by this question, it is not possible to state a number of hens which will produce exactly 6 eggs in 6 days.


Yes, I've taken a simple math problem and tied it in a logical knot. One of my pet peeves is vague word problems that -could- be trick questions about logic, or they -could- be simple math problems.

I imagined myself in an actual interview, answering with the obvious "1.5 hens," only to be told in that we're-so-clever voice that I'm wrong because (pick one):
- half eggs don't count
- half a hen is a dead hen
- given those assumptions, there is no answer
- it doesn't matter because we like asking vague questions during interviews. That way, no matter what candidates say, we can tell them that they're wrong, hopefully making them feel insecure, and that makes salary negotiations so much easier. ;-)


Chris Lichti
Sunday, March 24, 2002

I agree the question is somewhat on the trick side (hence the high aha! rating).

I think its not very appropriate to ask it as an interview question except in hopes that the interviewee gives the answer you gave which shows they can actually think.  If an interviewer asked it in hopes of getting the answer given and then said "No, you are wrong" then you probably don't want to work with that weenie anyway.

Michael H. Pryor
Sunday, March 24, 2002

Ah.  So in other words, number problems are a test of the interviewee; logic problems are a test of the interviewER.  :-)

Paul Brinkley
Monday, March 25, 2002

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