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Todays question, ...

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North Pack:
Today's   Question - Sam comes downstairs to learn there is a power blackout.  He has no watch and the grandfather clock wound down two days ago.    He rewinds the grandfather clock and sets it to noon (a guess).   He's due at Bob's house for lunch.  He walks down the country road   to Bob's and discovers that Bob has the blackout problem too - Bob has a watch.  Sam asks the time, they have lunch and as Sam is leaving   he asks the time again.  He discovers he's been there for 1 1/2 hours.  Once home, he looks at the grandfather clock and resets   it to the correct time.  Assuming the power is still out and Sam is still watch-less - how does he know the time?

Big_Bill:
Sam turned on his emergency radio, and reset the clock !

Bill :)

North Pack:
Dunno Bill, - could well be. Grabbed this off another site, I won't have the answer until tomorrow. Unless someone here comes up with it.  "Hopefully" they'll post the answer tomorrow.

Motodad:
How does this sound. He set the clock to 12:00 but it really doesn't matter what time it is set for. When Sam leaves Bob's house he knows what time it is. When he gets home he can look at the clock to see how long he has been gone, subtract the 1 1/2 hours he knows he was at Bob's. Now he knows how long it took him to walk there and back. He knows what time it was when he left Bob's place and now he knows how long it took him to walk home. With some simple math he can set the grandfather clock to the right time.

TCups:
Let's see. . . what does Sam know?  

A. He knows the total time elapsed since he set the GF clock/left his house and the time he returned, reset the GF clock.

B. He knows the correct time when he arrived at Bob's place.

C. He knows the correct time when he left Bob's place.

D. He knows the elapsed time he spent at Bob's place.

E. He knows the difference between (A-D)/2 = the time it took to walk one way (to or from) Bob's.


It is daylight -- Sam guessed around noon, and they were having lunch, not breakfast or dinner.


Questions:  

He has to come "down" stairs to learn the power is out.  Is that important?  No.
It has been two full days since the GF clock wound down.  Is that important?  No
He walks down a "country road".  Is that important? Yes.  Bob must walk at a constant speed, which, I suppose, is more likely on a country road than in a city with traffic, stop lights, and crosswalks, etc.
The blackout is at both Sam's and Bob's houses.  Is that important?  No.
Sam knows whether or not he was at Bob's house at noon or not (presuming Bob's watch correct).  Is that important?  No.  The arithmetic works day or night.

Lets say Bob was gone 2 hours on the GF clock and spent 90 minutes at Bob's house.  He has a accurate measurement of both elapsed times.

Lets say he arrived at Bob's at 11:30 AM and left at 13:00 (Bob told him so).

So, 2 hours elapsed since Bob left his house and came back.  1.5 hours at Sam's house.  The difference, 30 minutes, it the time to walk both ways, and half that, 15 minutes is the time it takes him to walk home.

So, if he left Bob's at 13:00 and it took him 15 minutes to walk home, then the correct time would be 13:15, but his GF clock would show 14:00 (noon plus 2 hours), so he would have to turn the GF clock back 45 minutes.

:)

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