Brainteaser and math puzzle thread - Page 8 - Puzzles and Other Games Forum

Nevermind lol.

After looking at your explanation (you did it basically the same way as me, just with way less brute force) it appears I am actually right.

You made a tiny error at the end.

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07-11-2011 , 05:36 PM

#178

ibavly

2010 PSOP Champion

Join Date: Feb 2010 Posts: 24,513

I see that has already been pointed out.

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07-11-2011 , 06:47 PM

#179

pwnsall

CFBBPC

Join Date: Jun 2006 Posts: 65,885

these brainteasers suck

i remember crossnumber puzzles being reasonably enjoyable if anyone knows of decent ones

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07-11-2011 , 06:51 PM

#180

ibavly

2010 PSOP Champion

Join Date: Feb 2010 Posts: 24,513

you have a house with 66 wires going from the bottom floor to the top floor, but you don't know which top corresponds to which bottom. the only tool you have is a battery with a light. You play around with the wires on the main floor, go up and play around with the wires on the second floor, come back down and play around with the wires on the main floor, and you know which wire is which.

What did you do?

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07-12-2011 , 02:50 AM

#181

FCBLComish

Carpal \'Tunnel

Join Date: Sep 2005 Posts: 21,060

Quote:

Originally Posted by bojtun

NO ****ING RESEARCH or spoils for ppl who know!!!

jackl and jill went up the hill eachj with a buck nd a quaryer ... what happened?

Spoiler:

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07-12-2011 , 11:18 PM

#182

ibavly

2010 PSOP Champion

Join Date: Feb 2010 Posts: 24,513

You invest in a mining operation that costs you 10k. After 1 year you receive a lump sum of 23k. After one more year you have to pay a clean up cost of 13.2k. What is your yield on the investment?

Just did this problem today, and the answer is very surprising.

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07-13-2011 , 03:24 AM

#183

Gabethebabe

Malware Jedi

Join Date: Oct 2007 Posts: 27,550

Quote:

Originally Posted by ibavly

This was in Chile?

I don´t get the problem btw. You lose $200

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07-13-2011 , 03:27 AM

#184

ibavly

2010 PSOP Champion

Join Date: Feb 2010 Posts: 24,513

yield is a %. And it's not negative in this case

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07-13-2011 , 10:45 AM

#185

brrrrr

Pooh-Bah

Join Date: Dec 2009 Posts: 4,371

We don't need interest rates to answer this?

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07-13-2011 , 11:38 AM

#186

ibavly

2010 PSOP Champion

Join Date: Feb 2010 Posts: 24,513

nope, its the internal rate of return

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07-13-2011 , 11:57 AM

#187

brrrrr

Pooh-Bah

Join Date: Dec 2009 Posts: 4,371

Oh right. I was thinking NPV. Haven't done this stuff in years.

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07-13-2011 , 02:49 PM

#188

brrrrr

Pooh-Bah

Join Date: Dec 2009 Posts: 4,371

OK, I've had some time to think about this and play with the numbers. IRR is a terrible measure for this problem.

The answer ibav wants is

Spoiler:

however, let's increase the final clean up cost to $13,220, ie we lose more money picking up after ourselves. The result?

Spoiler:

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07-13-2011 , 04:59 PM

#189

ibavly

2010 PSOP Champion

Join Date: Feb 2010 Posts: 24,513

Spoiler:

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07-13-2011 , 06:04 PM

#190

brrrrr

Pooh-Bah

Join Date: Dec 2009 Posts: 4,371

Is this your financing homework or something?

The graph would shift left meaning that at the same discount rate, the NPV would be higher.

edit: er, it's a negatively sloping graph, so maybe i'm backwards. either way cashflows would have to be more positive n0 or n1 i think.

edit2: yeah im backwards i think. graph shifts right.

Last edited by brrrrr; 07-13-2011 at 06:07 PM. Reason: more positive cash flows in n0 or n1

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07-13-2011 , 06:10 PM

#191

ibavly

2010 PSOP Champion

Join Date: Feb 2010 Posts: 24,513

I was studying for the actuarial exam and I found it really interesting that it is possible have a single cashflow function with two different correct yields.

10%:

t=0: -10k -> t=1: -11k + 23k = 12k -> t=2: 13.2k-13.2k=0

20%

t=0: -10k -> t=1: -12k + 23k = 11k -> t=3: 13.2k-13.2k=0

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07-13-2011 , 06:20 PM

#192

brrrrr

Pooh-Bah

Join Date: Dec 2009 Posts: 4,371

I see. cashflows stay the same but the change in cashflows is greater. that is cute.

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07-12-2012 , 04:00 AM

#193

ibavly

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Here's a fun one

You have n coins. Each coin is blue on one side red on the other. m of them start on the red side and n-m on the blue side.

n and m are known

you get blindfolded, and can now move the coins around, flip them etc., but obviously you have no way of knowing which coin you are touching.

You have to split all the coins in to 2 piles, such that each pile contains an identical number of red faces showing.

How do you do this?

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07-12-2012 , 06:57 AM

#194

Gabethebabe

Malware Jedi

Join Date: Oct 2007 Posts: 27,550

Impossible with current description. I can't even do it with 4 coins that are 3-1 divided between red and blue. You will need to flip one, but you could end up with piles of two red and two blue as well as two piles of one blue/red in each, since you cannot see anything before putting it into a pile.

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07-12-2012 , 07:07 AM

#195

Treep

veteran

Join Date: Oct 2011 Posts: 2,925

it's easy

Spoiler:

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07-12-2012 , 08:03 AM

#196

metsandfinsfan

banned

Join Date: Jan 2006 Posts: 159,821

yes that coin one is one of my alltime favs

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07-12-2012 , 08:13 AM

#197

Gabethebabe

Malware Jedi

Join Date: Oct 2007 Posts: 27,550

wow

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07-12-2012 , 12:58 PM

#198

Wyman

Carpal \'Tunnel

Join Date: Mar 2007 Posts: 13,041

http://itunes.apple.com/us/app/63-lo...500243153?mt=8

If you DL this add me on gamecenter bk<my_username>.

There are 1500+ puzzles in 63 puzzle types.

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07-17-2012 , 05:50 PM

#199

ibavly

2010 PSOP Champion

Join Date: Feb 2010 Posts: 24,513

A couple more

You have 5 coins, one of them weighs a different amount. You have a standard electronic scale, and you can use it 3 times. How do you find out a - which coin is different b - how much does it weigh

0, 2, 24, 252, 3120, ... what comes next

9, 10, 11, 12, 13, 14, 21, 100, ...

Prove that N = n(n+1)(n+2)(n+3)+1 is a perfect square for any whole number n

Last edited by ibavly; 07-17-2012 at 06:01 PM.