crazy brain teasers ...

[nyker96]

(1) A Sultan ordered ten goldsmiths to make ten coins each. Each
coin was to weigh exactly ten grams of pure gold.
One of the goldsmiths was a bad man. He decided to cheat. He
made all his ten coins one gram short. Now the Sultan heard that
one of the goldsmiths had cheated. He also heard that this man
had made each of his coins 1 gram short.

So what's the minimum number of weighing needed for the
clever Sultan to find out the culprit?

Note: Not balance scale but a weight scale i.e. tells you number of grams.

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(2)
ok, since you dudes so bright, here's a tougher one I just remembered:
If you given 2 NON-UNIFORM candles, all we know is each can be burnt in 1 hour's time.
How can you use them to time 45min?

=====

(3) Thanks to ... illusion88
You are asked to find the height of a very tall building. The only equipment you are given is a very expensive, very percise barometer and a watch. Tell me three ways to find the height of the building using the barometer the watch.

 

[mordantmonkey]

weighed them together once only? that's too ambiguous. meaning i could come up with many solutions that would fit that loose description.

was this using a balance? a triple beam with a numerical indicator?

 

[hypn0tik]

------------ SPOILER ---------------------































Old.

Took 1 coin from the first
Took 2 coins from the second
Took 3 coins from the third
and so on...

If he was off by x grams from what he expected, the xth goldsmith was the thief.

 

[GoingUp]

Took 1 from the first, two from the second etc.

Whatever number you end up in the ones place, subtract 10- that number and you have your cheat.

 

[bsobel]

10 coins from the first, 9 from the second, 8 from the third etc. When measured the numbers of ouces off (e.g. for example 4) was the person who gave that many.

 

[nyker96]

damn you dudes pretty slick. Ok, put one up here that's tougher!!! and I'll add yours to top!

More challenges people!!

 

[bsobel]

Does the plane take off? 😉

 

[illusion88]

You are asked to find the height of a very tall building. The only equipment you are given is a very expensive, very percise barometer and a watch. Tell me three ways to find the height of the building using the barometer the watch.

EDIT: this is actually a Cisco interview question, two answers should be obvious, the third is a bit harder to find.

 

[nyker96]

I already got 2x ways illusion88. but will wait a bit to post them... in mean while third way ...

 

[bsobel]

Originally posted by: illusion88
You are asked to find the height of a very tall building. The only equipment you are given is a very expensive, very percise barometer and a watch. Tell me three ways to find the height of the building using the barometer the watch.

EDIT: this is actually a Cisco interview question, two answers should be obvious, the third is a bit harder to find.

The 4 famous ways: Direct determnation based on preasure measurements at top bottom. Drop the barometer, time it with watch. Sun dial approach (height of barometer vs height of buildng).

And my favorite. Knock on the supers door and say 'if you tell me the height of the building I will give you this barometer' 😉

 

[nyker96]

but bsobel how do you know the height of the barometer? you ain't got no ruler? ...

I do accept the other 3 tho. nicely done. Must say you guys really quick minded.

ANy1 got the cadle problem I posted?

 

[yankeesfan]

Cut the last fourth off of one of the candles

 

[nyker96]

yankeesfan, been a surgeon you probably would be use to cutting ... but in this case the candle is NON-uniform.

 

[TuxDave]

(2) Assuming you can lay the candle sideways and burn the other end.

Burn both ends of candle #1 and one end of candle #2.

When candle #1 is burned out, 30 minutes will have passed and 30 minutes remain on candle #2.

Burn the other end of candle #2 and that will burn out in 15 minutes.

 

[nyker96]

TuxDave excellent! You the man ...

 

[oCxTiTaN]

Pretty good 😉

 

[DrPizza]

You are asked to find the height of a very tall building. The only equipment you are given is a very expensive, very percise barometer and a watch. Tell me three ways to find the height of the building using the barometer the watch.

Method 1: drop the barometer from the top of the building. Time its decent. Use d=1/2 a t^2 to calculate the time. If that's not good enough for you, then assume drag is proportional to velocity squared... differential equations... Still no big deal.

Method 2: Find the building superintendent and say "If I give you this barometer and watch, will you tell me how tall the building is?"

 

[Viperoni]

Originally posted by: TuxDave
(2) Assuming you can lay the candle sideways and burn the other end.

Burn both ends of candle #1 and one end of candle #2.

When candle #1 is burned out, 30 minutes will have passed and 30 minutes remain on candle #2.

Burn the other end of candle #2 and that will burn out in 15 minutes.

I hope that

NON-UNIFORM candles

doesn't mean they don't burn at constant rates, becuase if so, TuxDaves' solution would not work.

 

[Born2bwire]

Originally posted by: Viperoni

Originally posted by: TuxDave
(2) Assuming you can lay the candle sideways and burn the other end.

Burn both ends of candle #1 and one end of candle #2.

When candle #1 is burned out, 30 minutes will have passed and 30 minutes remain on candle #2.

Burn the other end of candle #2 and that will burn out in 15 minutes.

I hope that

NON-UNIFORM candles

doesn't mean they don't burn at constant rates, becuase if so, TuxDaves' solution would not work.

No, TuxDave's solution works. This is a common teaser so you can probably easily find it via google. But suffice to say, the non-uniformity of the rate of burning does not affect his results because Tux waits for an entire candle to extinguish to mark his time.

 

[nyker96]

I used to know a HS teacher, he is rumored to have an IQ of 180. So we took turns giving him brain teasers, you know what the guys gets it every time ... just a story.