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Macavity

The correct answer, in my opinion, is two with a spring scale and one with a balance scale.

Why?

Because if you weigh one pool ball on a spring scale and the next one you weight is lighter/heavier, you've found the rigged ball.

With a balance scale, you only have to weigh one ball against another - and again, if one ball is heavier than another, you've found the rigged ball.

**Posted:** Mon Aug 08, 2005 6:39 pm

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**Posted:** Mon Aug 08, 2005 7:27 pm

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Christyxo · Guest

Actually Macavity has a point here.

If you picked up two balls and one happened to be the lighter one then you would only need the one weighing (and some luck to pick up the correct ball)

Since the question says what is the minimum I'll have to agree with Macavity. The question is asking for the minimum number only - not the most likly number of weighings.

**Posted:** Sun Aug 21, 2005 5:39 pm

Totally New to Perplex · Guest

To take things to an absurd extreme, one could argue that the moment he picks up the scales, four kids and a dog bust into the bar, grab Tone, pull off his mask and reveal Lenny Lightfoot, the notorious pool shark and scam artist, whose signature move is to place a lightened ball on the table when his opponent's back is turned. He screams, "And I'd have gotten away with it, too, if it weren't for you meddling kids!" The number of weighings, in this case, would be zero.

**Posted:** Sun Aug 21, 2005 5:55 pm

Zeina · Greenhorn Joined: 03 Sep 2005 Posts: 3 Location: Lebanon

Guys correct me if i'm wrong, but I think 2 weighings wont do it, that is if we need to prove beyond the shadow of a doubt that there's a lighter ball (but then the question is a bit ambiguous on that). Here's why I think nmarciano & JebJoya's answers are a bit flawed:

1) WEIGH ( 123 ) AGAINST ( 456 )
If equal go to step ( 2 )
If ( 123 ) lighter go to step ( 3 )
If ( 456 ) lighter go to step ( 4 )

2) WEIGH ( 7 ) AGAINST ( 8 )
If equal, BALL 9 is the LIGHT one (that's speculation, not proof)
If ( 7 ) lighter, BALL 7 is the LIGHT one
If ( 8 ) lighter, BALL 8 is the LIGHT one

3) WEIGH ( 1 ) AGAINST ( 2 )
If equal, BALL 3 is the LIGHT one (again, speculation)
If ( 1 ) lighter, BALL 1 is the LIGHT one
If ( 2 ) lighter, BALL 2 is the LIGHT one

4) WEIGH ( 4 ) AGAINST ( 5 )
If equal, BALL 6 is the LIGHT one (speculation)
If ( 4 ) lighter, BALL 4 is the LIGHT one
If ( 5 ) lighter, BALL 5 is the LIGHT one

Please help!!!

**Posted:** Sat Sep 03, 2005 1:13 am

ParityBit

I see what you're saying Zeina, but I think that it would only be an issue if the idea of one ball lighter than the others was not confirmed.

If we know for definite that there is one ball lighter, then two weighings could find it. If you it's only a possibility that one ball is lighter, then an additional weighing would be necessary.

In this type of puzzle, I think that the idea of the lighter ball is a given, so I would go along with two weighings.

**Posted:** Sat Sep 03, 2005 6:58 am

Da Tee In TeeS of doom · Boot Joined: 12 Sep 2005 Posts: 30 Location: Denmark

that easy?

**Posted:** Mon Sep 12, 2005 6:47 pm

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Rob_Riv · Unfettered Joined: 17 Feb 2005 Posts: 350

Okay The answer has already been posted it's...

1) WEIGH ( 123 ) AGAINST ( 456 )
If equal go to step ( 2 )
If ( 123 ) lighter go to step ( 3 )
If ( 456 ) lighter go to step ( 4 )

2) WEIGH ( 7 ) AGAINST ( 8 )
If equal, BALL 9 is the LIGHT one
If ( 7 ) lighter, BALL 7 is the LIGHT one
If ( 8 ) lighter, BALL 8 is the LIGHT one

3) WEIGH ( 1 ) AGAINST ( 2 )
If equal, BALL 3 is the LIGHT one
If ( 1 ) lighter, BALL 1 is the LIGHT one
If ( 2 ) lighter, BALL 2 is the LIGHT one

4) WEIGH ( 4 ) AGAINST ( 5 )
If equal, BALL 6 is the LIGHT one
If ( 4 ) lighter, BALL 4 is the LIGHT one
If ( 5 ) lighter, BALL 5 is the LIGHT one

The scales are described as 'REGULATION WEIGHING SCALES' which are balance scales.

So Answer is...

**Posted:** Tue Sep 13, 2005 3:06 pm

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M. Johansson · Veteran Joined: 07 Oct 2003 Posts: 79

Um, what if you start out by weighing 8 balls, 4 in each scale, and the two sets of four turned out to be equal? That would mean that the 9th ball would be the one that is off.

Of course, that doesn't PROVE that that one is off (the 9th could still be the same weight as all the others, if the storyteller on the card is wrong about the balls), but that is not exactly what the card is asking for - it asks for which one is lighter, not IF one is lighter.

So: 1.

**Posted:** Tue Sep 13, 2005 5:26 pm

joshF

To be honest, i don't think there should be much complication here. If we are looking at working with balance scales, then the minimum amount of weigh ins would definitely be one. Because there is a chance that you will pick the tampered and normal ball, and be able to see which is lighter. And of course u cant have weigh in of less than one so this seams the answer Wink

.

**Posted:** Mon Oct 03, 2005 5:28 pm

Rob_Riv · Unfettered Joined: 17 Feb 2005 Posts: 350

I still think it's 2. Wink

**Posted:** Mon Oct 03, 2005 5:37 pm

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Sheepnumber12 · Boot Joined: 18 Oct 2005 Posts: 12 Location: England

It would take a minimum of 2 weighings.

1st weighing: Lightest ball
2nd weighing: Normal ball

Also, just under the scratch-off area, the darkness is lighter. Can anyone find anything in this area?