Can I Install Ubuntu first before installing Windows for dual boot
To use Windows and Ubuntu on one computer, which should I install first?
A deck of 52 cards is shuffled, and we deal a bridge of 13 cards. Let $X$ be the number of aces and $Y$ be the number of spades. Show that $X$, $Y$ are uncorrelated.  Here is what I did:  $Cov(X,Y) = E[XY]-E[X]E[Y]$   uncorrelated means $Cov(X,Y) = 0$, hence  $E[XY]=E[X]E[Y]$   $E[X] =  \sum_{k=0}^{k=4} k \frac{\dbinom{4}{k} \dbinom{48}{13-k}}{\dbinom{52}{13}} $   $E[Y] =  \sum_{k=0}^{k=13} k \frac{\dbinom{13}{k} \dbinom{39}{13-k}}{\dbinom{52}{13}} $   Are the summations above correct? and how do I calculate $E[XY]$? What are the differences between 32-bit and 64-bit systems?  If you have used both of them, what kind of sharp differences have you experienced?   Would it be a problem to use 32-bit programs on 64-bit systems in some cases? Are there any areas that should be avoided and are there any steps I should take to protect myself from radiation? How can Cooper communicate with his daughter before the time he went to space? How to enable or disable a user? I'm uing ubuntu 12.04 desktop. I have 3 users: user1(administrator), user2(standard) and guest. I wanted to disable user1 and enable user2 which auto logs on with no password but after I did that I can't login to user1 and user2 accounts except the guest session user. I'm striped off every administrative privileges. I don't know which options are available to me and how do I enable root or user which is an administrator? Possibility of recovering files from a dd zero-filled hard disk I have "zero filled" (complete wiped) an external hard disk using dd, and from what I have heard: people said you should at least "zero fill" 3 times to be sure that the data are really wiped and no one can recover anything.  So I decided to scan the disk once again after I've zero filled the disk. I was expecting the disk to still have some random binary left. It turned out that it has only a few sequential bytes in the very beginning. This is probably the file structure type and other headers stuff. Other than that, it's all zeros and nothing else.  So if we have to recover any file from a zero filled disk, ...how? From what I've heard, even you zero fill the disk, you should still have some data left. ...or could dd really completely annihilate all data? I am using tufte-latex package, which uses mathpazo with old style numerals. To make figures (plots) I would like to use lining numbers.  The problem is that the figures are converted from svg to pdf using inkscape and the numbers are not in mathmode (In math mode the numbers are lining numerals by default).  I think of two possible solutions:  a) Is there any command similar to \oldstylenums that does the opposite work?  b) inkscape put the text of the figure in \smash{-22.22} commands. Is any way,  using sed, awk, perl,... to change that to \smash{$-22.22}? Every differentiable function $f:R \rightarrow R$ with the property that $(2h)f′(x) =f(x+h)−f(x−h)$ for all $x \in R$ and all $h$ has the form $f(x) =ax^2+bx+c$.  I would like to get some help on this one. Taking partial derivatives was an idea, but is that legal? Simple logic problem: Finding largest and smallest number among 3 numbers Java conditional compilation: how to prevent code chunks from being compiled? I have been using Ubuntu 12.04 for quite a while and have never had a problem come at me out of the blue like this. I'm trying to install python 3.2 on my Ubuntu system and every time I run the code to compile the python source, I get this error:  'Command 'sudo' is available in '/usr/bin/sudo' The command could not be located because '/usr/bin' is not included in the PATH environment variable. sudo: command not found'   I've also tried running gksudo command to view what my environment shows but I pretty much get the same error. The work done against gravity is $mgh$, well at least that's what my textbook says. I have a question: I can apply a force say 50N, so total work done = $mgh + mah$. Where $ma$ = Force. But the truth is irrespective of the force applied, the work done against gravity is always $mgh$. Why?  For example, when I move an object with a force, the work done is more, so work depends on the Force. But in case of gravity it always depends upon the weight How do I vertically center a single cell within a table? Can I run Android apps on Ubuntu? (This question is meant to be a resource to direct others to given that this is a common question.)  Given the task of creating an image that will be printed at a certain size, what pixel dimensions and resolution should I be setting my file at? I'm just starting to learn linear algebra and I understand Gaussion elimination but I don't understand this proof:    Is the heart of this the fact that all the while when I've been row-reducing matrices to reduced row-echelon form... I've actually been multiplying a matrix by a series of a elementary matrices?  What does the notation $[A\ \ 0]$ mean?  How is the equation $A = E_1^{-1}...E_k^{-1}$ arrived at? I am a PhD student in mechE. After paying the first year tuition out of pocket, I accepted a PhD project due to desperation for funding. However, after an year I realized that I hate the project. Here I made a mistake of not leaving/changing the project, I just waited out hoping I would like the project. I also asked my advisor a couple for a different project and he did not want to change my project due to sponsor obligations. For some reason I couldn’t assert myself and stayed on. However my hate for the project only grew with time and now I am in my fifth year. I have reached a stage where I absolutely hate the project and don’t know what to do. I can hardly do any work. I feel like quitting everyday and still feel it is wrong to quit this late. I have a very substandard thesis. I am lost and feel stuck, please advise on what to do. Thanks How do you square an ideal? For some of you, this question is going to seem extremely basic.  I think I understand what an ideal is. Such as $\langle 2, 1 + \sqrt{-5} \rangle$, it consists of all numbers in this ring of the form $2a + (1 + \sqrt{-5})b$.  But then what is $\langle 2, 1 + \sqrt{-5} \rangle^2$? My first thought was $\langle 4, -4 + 2 \sqrt{-5} \rangle$, but that seems wrong somehow. I also had something in the back of my mind saying $\langle 2 \rangle$, but I'm not sure about that one either.  Then I thought about trying to figure out $\langle 2, 1 + \sqrt{-5} \rangle \langle 2, 1 + \sqrt{-5} \rangle$ when I realized I don't actually understand how to multiply ideals to begin with.  I'm only using $\langle 2, 1 + \sqrt{-5} \rangle$ as an example (though that does draw in one question identified as similar that looks much more relevant than all the questions identified as "Questions that may already have your answer"). In a principal ideal domain, would it be correct to think that $\langle a \rangle \langle b \rangle = \langle ab \rangle$?  Any help would be much appreciated. Does editing still bump a question? Many times in the past I've edited a somewhat recent answer—say, from 30 minutes ago—and noticed that the concomitant question didn't bump to the top.  I just confirmed it with ; the question is currently sorted in the JavaScript page based on when it was asked, not my edit.  I've never made edits just to bump a question to whore rep—my original answer was wrong which was why I fixed it—but my understanding is that the CW self-edit trigger exists to prevent  edit-then-bump-then-score-rep—profit! activity.    If non-ancient edits no longer bump a question, should the self-edit CW trigger be brought inline with this?  Should an answer be made CW if you make 10 edits that actually bump the question?  and to avoid any implication of impropriety, I'm already capped on SO, so I'm not looking for any sort of "meta effect" on my answer Shiny locked Legendaries in ORAS Serebii says that (probably) the only  in ORAS are Kyogre, Groudon, Rayquaza and Deoxys. This means that Reshiram and Zekrom, that were shiny locked in BW/B2W2, now can be found shiny.    Can anyone prove this? I'd like to know if it's true before waste hours in softresetting.