Official Trivia/Riddles/Lateral Thinking Thread

[Calliander]

Well in that case you wouldn't really need the scale. I mean, one bag would weight twice that of the others and it'd be pretty easy to spot, I reckon.

How is that? You'd have to do two weighings.

[red_war_machine]

How is that? You'd have to do two weighings.

I mean, just by holding them.

[SearchManX]

Alright.

I hope Regus isn't looking for one right now. Maybe he can post his no matter who gets mine. Anyway.

A man has ten bags of coins which all look alike. One of the bags is filled with fake coins. All the genuine coins weigh 10 grams each and all the fake coins weight 20 grams each. Each of the ten bags contain 20 coins. Using a scale which measures in grams, how would he be able to determine which bag contains the fake coins with only one weighing?

You take 1 coin from the first bag, 2 from the second, 3 from the third, etc... and weigh them. Since only 1 bag has fake coins, 9 bags are real, meaning 90 grams are real. Subtract 90 from your total weight, and divide by 20, and the number you get is the amount of coins you got from x bag, meaning its the fake one.

[MVS]

I omitted the :P

Does that make you feel better?


(:P)

[Curtis]

I'd put the heaviest bag there on the scale first... But I know that is not the answer.

[MVS]

You take 1 coin from the first bag, 2 from the second, 3 from the third, etc... and weigh them. Since only 1 bag has fake coins, 9 bags are real, meaning 90 grams are real. Subtract 90 from your total weight, and divide by 20, and the number you get is the amount of coins you got from x bag, meaning its the fake one.

That sounds pretty good. I have no idea if it's right, but it's better than I could ever come up wtih.

[Calliander]

You take 1 coin from the first bag, 2 from the second, 3 from the third, etc... and weigh them. Since only 1 bag has fake coins, 9 bags are real, meaning 90 grams are real. Subtract 90 from your total weight, and divide by 20, and the number you get is the amount of coins you got from x bag, meaning its the fake one.

I see where you're going with this, but here:

1 coin from first bag: 10 grams
2 coins from second bag: 20 grams
and so on

I think you're assuming they're 1 gram each. The real ones are 10 grams and the fake ones are 20 grams. You're close.

[MVS]

Are you positive it's only one weighing?

I think I've seen variations on this with 3 weighings.

[red_war_machine]

You take 1 coin from the first bag, 2 from the second, 3 from the third, etc... and weigh them. Since only 1 bag has fake coins, 9 bags are real, meaning 900 grams are real. Subtract 900 from your total weight, and divide by 200, and the number you get is the amount of coins you got from x bag, meaning its the fake one.

[Calliander]

Are you positive it's only one weighing?

I think I've seen variations on this with 3 weighings.

Nope, one weighing. I have the riddle and solution in front of me.