Brain bleeder!

[JayC9]

I took a job aptitude test yesterday and this was one of the questions on the paper.

Personally I think it's a c*nt of a question and I must admit that I didn't work it out till I'd gotten home.


9 identical balls. 8 balls are exactly the same weight. 1 ball weighs more than the others.

Using a balance scale only twice how can you find out which ball is heavier?


Major respect and a whopping 1 karma point to the first person to figure it out.

 

[JayC9]

So I'm safe to assume that I'm not the only dummass on this forum.

You tellin me nobody knows the answer?

 

[hamstershaver]

pick them all up with your hand and you should be able to tell that way

 

[JayC9]

pick them all up with your hand and you should be able to tell that way

UUMMMHHHH

Can't do that. Re-read. Got to use the balance.

 

[westsnoop]

Seperate the balls into 3 groups of 3, weigh two of the groups on the scales if one is lighter than the other you know it has the lighter ball if they're the same the third group has the lighter ball. For the second weighing take the group of 3 you know has the lighter ball and do the same by weighing 2 of the balls and if one is lighter its that one or if their the same it's the third.

 

[bullett]

OK Jay, lets reason this out...

Its easy to get to four balls. Set one out, put four on each side, if the scale balances, the ninth ball is it, if it doesn't balance, then your are down to one of four....

Then....

 

[ChefWide]

Seperate the balls into 3 groups of 3, weigh two of the groups on the scales if one is lighter than the other you know it has the lighter ball if they're the same the third group has the lighter ball. For the second weighing take the group of 3 you know has the lighter ball and do the same by weighing 2 of the balls and if one is lighter its that one or if their the same it's the third.

we have a winner...


Now do it for 12 balls....

 

[JayC9]

Seperate the balls into 3 groups of 3, weigh two of the groups on the scales if one is lighter than the other you know it has the lighter ball if they're the same the third group has the lighter ball. For the second weighing take the group of 3 you know has the lighter ball and do the same by weighing 2 of the balls and if one is lighter its that one or if their the same it's the third.

Spot on Einstein!!!

Did you get that straight away?

 

[ChefWide]

Spot on Einstein!!!

Did you get that straight away?

google search turned it up on the first try...

 

[JayC9]

google search turned it up on the first try...

Tellin you....it's scary doing tests all over again! Especially when there's younger guys doing the same test. They're used to doing tests and it's like you've got to prove yourself.

 

[bullett]

we have a winner...


That..

 

[Deterass]

 

[Lestat]

three groups of 3.


This is hardly a brain bleeder..

 

[hamstershaver]

UUMMMHHHH

Can't do that. Re-read. Got to use the balance.

how do you get them in the balance if you cant pick them up?

 

[bullett]

how do you get them in the balance if you cant pick them up?

Balls, Balls, Balls

 

[JayC9]

how do you get them in the balance if you cant pick them up?

Hypothetical question. No physical limitation.

 

[westsnoop]

google search turned it up on the first try...

Ratted me out!

 

[geoboy]

wests answer is better, but I was gonna say

1) weigh 4 and 4,
if they're balanced, its the 9th ball, if the scale isnt balanced,
2) remove 1 ball from each side until the scales balance. one of the balls just removed would be the heavier one. This completes one "use" of the scale.
3) now remove all the remaining balls and place the 2 identified balls on the scale to see which is heavier.

liberal interpretation of "use the scale twice"