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SpeedRacer

The Brainteaser thread

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Here's a brainteaser, what does your screenname mean? ;)



My 2 yr old called me a "coo-t-pie" one night and that's what came to mind when choosing a screen name. I used "Pi" because I'm a math teacher.



--
A mind that is stretched by a new experience can never go back to its old dimensions. -Oliver Wendel Holmes

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Why is a man-hole cover round?

This was actually an interview question I had once.

Hook



Because man-holes are round. Why would you put a square cover on a round hole?



Actually, that is a common interview question, and there's a lot of right answers. It's more to see how you think than anything.
Possible answers I've heard:
So it doesn't fall through (and probably the most correct)
Because the holes are round (easier to make circle than a square/more efficient use of space and material/whatever)
So you can handle the cover better - roll it to move it if you have to
Less possibility of snaging something (corners of a square could pinch something)
Couple others that I can't think of at the moment...
it's like incest - you're substituting convenience for quality

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Speaking of interview questions - this is supposedly one Microsoft has been known to ask:

"U2" has a concert that starts in 17 minutes and they must all cross a bridge to get there. All four men begin on the same side of the bridge.
You must help them across to the other side. It is night.

There is one flashlight. A maximum of two people can cross at one time. Any party who crosses, either 1 or 2 people, must have the flashlight
with them. The flashlight must be walked back and forth, it cannot be thrown, etc. Each band member walks at a different speed.

A pair must walk together at the rate of the slower man's pace:

Bono:- 1 minute to cross
Edge:- 2 minutes to cross
Adam:- 5 minutes to cross
Larry:-10 minutes to cross
it's like incest - you're substituting convenience for quality

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Yeah, I'm a brain teaser junkie. Here's another one - I'd say a good 75% of the people I've shown it to, don't figure it out without some kind of help.

1
11
21
1211
111221


What's the next line?
it's like incest - you're substituting convenience for quality

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It takes them 19 minutes to cross.

10 & 1 goes across = 10 minutes
1 comes back = 1 minutes
5 & 1 goes across = 5 minutes
1 comes back = 1 minutes
2 & 1 goes across = 2 minutes

now 10 + 1 + 5 + 1 + 2 = 19 minutes total

Edit: I guess they arrive 2 minutes late! LOL! :D

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I've always thought these kinds of things are not very fair. A solution to the puzzle should "feel" right, and you just don't feel right about the solution to this one. I've actually seen people who got it but dismissed the solution because it didn't seem right.

-- Toggle Whippin' Yahoo
Skydiving is easy. All you have to do is relax while plummetting at 120 mph from 10,000' with nothing but some nylon and webbing to save you.

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A girl is locked in a room.
In the room there is a only baseball bat, a piano, and a saw.
This girl was clever enough to find three different ways out of the room by using these items.
What are the three ways out?




1. Saw the piano in half put the two halves together to make a whole, and climb through the (w)hole.
2. Ditto but with the bat.
3. Hit the piano with the bat to shake loose a key, then unlock the door with the key.

I fact, she didn't need the saw - she could have hit her toe with the bat to make it a little sore, and used that saw.

ANd having got out of the room, she should shout enough to make herself a little hoarse, and ride away on it.
...

The only sure way to survive a canopy collision is not to have one.

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A hole is drilled right through the center of a perfect sphere. The length of the hole is measured accurately using a micrometer. It is 2 inches. What is the remaining volume of material in the sphere?
...

The only sure way to survive a canopy collision is not to have one.

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You are in a room with three light switches, each of which controls one of three light bulbs in the next room. Your task is to determine which switch controls which bulb. All lights are off. Your constraints are: you may flick only two switches and you may enter the room with the light bulbs only once. How would you set about determining which switch controls which bulb?

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A hole is drilled right through the center of a perfect sphere. The length of the hole is measured accurately using a micrometer. It is 2 inches.


Didn't we do this one on here before?

For the light switch one - flip any two switches, wait awhile, flip one of the switches back off, go in the room. The bulb that's warm is the one you flipped off, the one that's on is the sitch you left on, the one that's off and cold goes to the switch you didn't touch.
it's like incest - you're substituting convenience for quality

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Can't really pay attention to this thread right now, but here's a mean one for you:

You have 12 steel balls (no jokes please). One of them is defective. It may be either heavier or lighter, you don't know. You have a balance scale but no weights, just the balls. Find the defective ball in exactly 3 measurements.

-- Toggle Whippin' Yahoo
Skydiving is easy. All you have to do is relax while plummetting at 120 mph from 10,000' with nothing but some nylon and webbing to save you.

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You drive your car from your home to a certain destination, at 60 mph. Then you drive back home at 40 mph. What is your average velocity overall?





Your velocity overall will be zero.

Velocity is displacement/time. Your displacement is zero, as you've ended up where you started from, and the time doesn't matter.

--
Arching is overrated - Marlies

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Can't really pay attention to this thread right now, but here's a mean one for you:

You have 12 steel balls (no jokes please). One of them is defective. It may be either heavier or lighter, you don't know. You have a balance scale but no weights, just the balls. Find the defective ball in exactly 3 measurements.


jesus christ that is mean... hang on, let me PM you my answer, see if anyone else can figure it out....

edit: nevermind, foudn a case where it doesn't work.

edit #2: I think I have it now! I'll send you the revised solution
it's like incest - you're substituting convenience for quality

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