Solve this equation for me - Page 4

MrRubix · 10-13-2009, 04:42 PM

Well it depends on what you want to do but yeah

**GG_Guru** · 10-13-2009, 04:43 PM

What was it that you wanted to do Marcus?

Umm, something about business right? I have a very foggy memory I can't remember squat sorry.

leonid · 10-13-2009, 04:43 PM

What did I do wrong lol
I just did E(profit) = $4 * .125 + ($-1) * .875 = $-.375

Wait, were you asking for expected profit or loss from trying to winning twice?

In that case, $-6... If this is wrong again, then I'll give up lol

**GG_Guru** · 10-13-2009, 04:44 PM

Dude get the **** out with that math problem lol.

Didn't you read my earlier post?

My unnecessary, over excessive post?

MrRubix · 10-13-2009, 04:45 PM

leonid: Hint: Since you know you'll win twice upon completion, let X = number of $1 tickets bought. Your profit is 10 - X since winning twice = 5*2 = 10 dollars -- you want to find E(Profit)

Yes you wanna find the E(Profit) of just winning twice in general (hence the question's phrasing)

EDIT: Yes -6 is right :P

Guru: Yes, I graduated from a business school, but I'm really a compsci dude at heart.

leonid · 10-13-2009, 04:46 PM

You win $4 for each winning tickets, because you get $5 but you already paid $1 for one..

edit: thanks for confusing me with problems that lack clarification >:0
edit2: I happen to know how to solve those problems as I'm taking intro to stats this semester lol

**GG_Guru** · 10-13-2009, 04:47 PM

Fellas, fellas..

The answer is obviously:

MrRubix · 10-13-2009, 04:48 PM

leonid: E(10-X) = 10 - E(X) = 10 - (2/.125) = -6

leonid · 10-13-2009, 04:49 PM

I did that while writing that post...

I don't know how to solve that problem you told us none of us will be able to figure out.. I tried the first part but I found myself having to solve a quintic polynomial inequality >_>

**GG_Guru** · 10-13-2009, 04:52 PM

HEY!

You guys wanna solve math problems?

Find the full value of pi.

Good luck I'll see you in forever minutes.

leonid · 10-13-2009, 04:54 PM

**GG_Guru** · 10-13-2009, 04:54 PM

+......?

RB_Killer · 10-13-2009, 04:54 PM

OMFG, are you srsly kidding me???? Some retarded 8th Grader can do this, I swear to god. (referring to GG-Guru's first post)

MrRubix · 10-13-2009, 04:55 PM

leonid: Alright, harder problem for you (I've always loved this problem -- was given to me in an interview).

You have a building with 100 floors, and you've got two glass spheres. These spheres are identical and breakable when dropped from a certain floor. For instance, if these spheres begin to break when dropped from floor X, that means they will also break any any floor above X and not break at any floor below X.

Once a sphere breaks, you lose that sphere. Develop an algorithm where you can guarantee me a maximum number of drops needed to find which floor is where the spheres' breakpoints are (it's possible that they'll survive even from floor 100).

Example: Worst algorithm: Start at floor 1, drop. If it doesn't break, drop from floor 2, etc... if the breakable floor was X=100, then that means you needed 100 drops.

**GG_Guru** · 10-13-2009, 04:55 PM

God damn it Rubix...
>.<

leonid · 10-13-2009, 04:58 PM

This is basically binary search >_>

Drop the glass ball from the 50th floor.. if it breaks, try to drop the ball from 25th, 13th, 7th, ...

If it doesn't break from 50th floor, try to drop it from 75th floor, etc

Maximum of ceil(log_2(100)) = 7 drops are needed

MrRubix · 10-13-2009, 04:59 PM

Quote:

Originally Posted by leonid

I did that while writing that post...

I don't know how to solve that problem you told us none of us will be able to figure out.. I tried the first part but I found myself having to solve a quintic polynomial inequality >_>

It is indeed a quintic polynomial inequality (but you're basically comparing a quintic to a cubic), but if done correctly, a lot of things will reduce nicely.

**Zipsnine** · 10-13-2009, 05:00 PM

You said that you answered that in an interview? So you were only able to use your head? No paper or pencil? In a certian amount of time?

MrRubix · 10-13-2009, 05:00 PM

Quote:

Originally Posted by leonid

This is basically binary search >_>

Drop the glass ball from the 50th floor.. if it breaks, try to drop the ball from 25th, 13th, 7th, ...

If it doesn't break from 50th floor, try to drop it from 75th floor, etc

Maximum of ceil(log_2(100)) = 7 drops are needed

what the **** lol if you could guarantee 7 drops, you would be God

So you drop from floor 50 -- it breaks. You try 25. It also breaks. You're out of spheres and you don't know the specific floor still -- binary search is a good place to start but since this approach does not work, it will hopefully give you a hint as to WHY it doesn't work and what kind of compensation is needed to offset its pitfalls.

MrRubix · 10-13-2009, 05:01 PM

Quote:

Originally Posted by Zipsnine

You said that you answered that in an interview? So you were only able to use your head? No paper or pencil? In a certian amount of time?

Yeah, no paper and pencil -- it took me about 15 minutes to figure out. Got the job, though.

10-13-2009, 04:42 PM	#61
MrRubix FFR Player Join Date: Dec 1969 Location: New York City, New York Posts: 8,340	Re: Solve this equation for me Well it depends on what you want to do but yeah __________________ https://www.youtube.com/watch?v=0es0Mip1jWY

10-13-2009, 04:43 PM	#62
GG_Guru Let em' do what they want Join Date: Mar 2006 Posts: 3,219	Re: Solve this equation for me What was it that you wanted to do Marcus? Umm, something about business right? I have a very foggy memory I can't remember squat sorry. __________________

10-13-2009, 04:43 PM	#63
leonid I am leonid Join Date: Oct 2008 Location: MOUNTAIN VIEW Age: 35 Posts: 8,080	Re: Solve this equation for me What did I do wrong lol I just did E(profit) = $4 * .125 + ($-1) * .875 = $-.375 Wait, were you asking for expected profit or loss from trying to winning twice? In that case, $-6... If this is wrong again, then I'll give up lol __________________ Proud member of Team No

10-13-2009, 04:44 PM	#64
GG_Guru Let em' do what they want Join Date: Mar 2006 Posts: 3,219	Re: Solve this equation for me Dude get the **** out with that math problem lol. Didn't you read my earlier post? My unnecessary, over excessive post? __________________

10-13-2009, 04:45 PM	#65
MrRubix FFR Player Join Date: Dec 1969 Location: New York City, New York Posts: 8,340	Re: Solve this equation for me leonid: Hint: Since you know you'll win twice upon completion, let X = number of $1 tickets bought. Your profit is 10 - X since winning twice = 5*2 = 10 dollars -- you want to find E(Profit) Yes you wanna find the E(Profit) of just winning twice in general (hence the question's phrasing) EDIT: Yes -6 is right :P Guru: Yes, I graduated from a business school, but I'm really a compsci dude at heart. __________________ https://www.youtube.com/watch?v=0es0Mip1jWY

10-13-2009, 04:46 PM	#66
leonid I am leonid Join Date: Oct 2008 Location: MOUNTAIN VIEW Age: 35 Posts: 8,080	Re: Solve this equation for me You win $4 for each winning tickets, because you get $5 but you already paid $1 for one.. edit: thanks for confusing me with problems that lack clarification >:0 edit2: I happen to know how to solve those problems as I'm taking intro to stats this semester lol __________________ Proud member of Team No

10-13-2009, 04:47 PM	#67
GG_Guru Let em' do what they want Join Date: Mar 2006 Posts: 3,219	Re: Solve this equation for me Fellas, fellas.. The answer is obviously: __________________

10-13-2009, 04:48 PM	#68
MrRubix FFR Player Join Date: Dec 1969 Location: New York City, New York Posts: 8,340	Re: Solve this equation for me leonid: E(10-X) = 10 - E(X) = 10 - (2/.125) = -6 __________________ https://www.youtube.com/watch?v=0es0Mip1jWY

10-13-2009, 04:49 PM	#69
leonid I am leonid Join Date: Oct 2008 Location: MOUNTAIN VIEW Age: 35 Posts: 8,080	Re: Solve this equation for me I did that while writing that post... I don't know how to solve that problem you told us none of us will be able to figure out.. I tried the first part but I found myself having to solve a quintic polynomial inequality >_> __________________ Proud member of Team No Last edited by leonid; 10-13-2009 at 04:52 PM..

10-13-2009, 04:52 PM	#70
GG_Guru Let em' do what they want Join Date: Mar 2006 Posts: 3,219	Re: Solve this equation for me HEY! You guys wanna solve math problems? Find the full value of pi. Good luck I'll see you in forever minutes. __________________

10-13-2009, 04:54 PM	#71
leonid I am leonid Join Date: Oct 2008 Location: MOUNTAIN VIEW Age: 35 Posts: 8,080	Re: Solve this equation for me __________________ Proud member of Team No

10-13-2009, 04:54 PM	#72
GG_Guru Let em' do what they want Join Date: Mar 2006 Posts: 3,219	Re: Solve this equation for me +......? __________________

10-13-2009, 04:55 PM	#74
MrRubix FFR Player Join Date: Dec 1969 Location: New York City, New York Posts: 8,340	Re: Solve this equation for me leonid: Alright, harder problem for you (I've always loved this problem -- was given to me in an interview). You have a building with 100 floors, and you've got two glass spheres. These spheres are identical and breakable when dropped from a certain floor. For instance, if these spheres begin to break when dropped from floor X, that means they will also break any any floor above X and not break at any floor below X. Once a sphere breaks, you lose that sphere. Develop an algorithm where you can guarantee me a maximum number of drops needed to find which floor is where the spheres' breakpoints are (it's possible that they'll survive even from floor 100). Example: Worst algorithm: Start at floor 1, drop. If it doesn't break, drop from floor 2, etc... if the breakable floor was X=100, then that means you needed 100 drops. __________________ https://www.youtube.com/watch?v=0es0Mip1jWY

10-13-2009, 04:55 PM	#75
GG_Guru Let em' do what they want Join Date: Mar 2006 Posts: 3,219	Re: Solve this equation for me God damn it Rubix... >.< __________________

10-13-2009, 04:58 PM	#76
leonid I am leonid Join Date: Oct 2008 Location: MOUNTAIN VIEW Age: 35 Posts: 8,080	Re: Solve this equation for me This is basically binary search >_> Drop the glass ball from the 50th floor.. if it breaks, try to drop the ball from 25th, 13th, 7th, ... If it doesn't break from 50th floor, try to drop it from 75th floor, etc Maximum of ceil(log_2(100)) = 7 drops are needed __________________ Proud member of Team No

10-13-2009, 05:00 PM	#78
Zipsnine FFR Veteran Join Date: Aug 2009 Location: Bushkill, P.A. Posts: 150	Re: Solve this equation for me You said that you answered that in an interview? So you were only able to use your head? No paper or pencil? In a certian amount of time?

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