posted on October 23, 2001 01:03:02 PM new
I found this on the PayPal site... and don't know the anwser (if there is one). Anybody?
You are given twelve balls. All are the same size and weight, except one which is heavier or lighter than the others. Using a balance scale, can you determine the odd ball in three weighings?
posted on October 23, 2001 01:41:48 PM new
Take the 12 balls and divide them into 3 groups of four and number them from 1-12
Step 1. - Compare 1,2,3,4 to 5,6,7,8. If they are equal, then the varying ball is in the third group of 9,10,11,12.
Step 2. - Compare 1,2,3 with 9,10,11 if equal, the answer is 12 and compare it to 1 to find out if it is heavier or lighter.
Step 3. - If step 2 is not equal then compare 9 and 10, if equal answer is 11. If step 3 is not equal choose the one that matches the fulcrum tilt in step 2.
Step 4. - If step 1 is not equal compare balls 1,2,3,5 to 4,10,11,12. You know from step one weather the tilt was heavier or lighter.
Step 5. - If step 4 is equal then compare 6 to 7, if it is equal the answer is 8 and it is the light one. If it is not equal take the lighter one of 6 & 7.
Step 6. - If step 4 was not equal and tilted down, compare 1 to 2, if equal the answer is 3 and it is heavy. If not equal choose the heavier of 1 & 2
Step 7. - If step 4 tilted down on compare 4 to 9, if equal then 5 is the light ball, if not then 4 is the heavy ball.
This is one of several solutions. My advice – go list some auctions and don’t bother with this stuff.
posted on October 23, 2001 03:01:12 PM new
I've always liked this one:
There are 4 men standing on one side of a bridge. It's dark, and between them, they only have one flashlight. The bridge is in bad condition, and it's only strong enough to hold two men at a time. In other words, two men go across, and one of them must bring the flashlight back to the remaining men.
Each of the men walks at a different speed.
Man #1 can cross the bridge in 1 minute
Man #2 can cross the bridge in 2 minutes
Man #3 can cross the bridge in 5 minutes
Man #4 can cross the bridge in 10 minutes
If, for example, Man #2 (2 minutes) and Man #4 (10 minutes) go across the bridge, they can only walk as fast as the slowest man. This pair would take 10 minutes to cross, then if Man #2 came back alone with the flashlight, that's 2 more minutes.
There is a 17 minute time limit to get all the men across.
There is no trick -- no one carries anyone else, or anything like that. And yes, it can be done.
(spelling)
[ edited by thedewey on Oct 23, 2001 03:03 PM ]
