Let $U_1$, $U_2$ and $U_3$ be i.i.d. $\mathsf {Uniform}[0,1]$ random variables. Find $P(U_1+U_2 &gt; U_3)$  Here the answer states that the probability is $\frac{5}{6}$. However I am quite confused as to how we obtain such an awnser. A hint is to use conditional expectation.  Any advice or explanation is apreciated.  I saw the following link :   And the key argument was the symetry of the system.
I'm trying to follow a line in a derivation for $P(Z&gt;X+Y)$ where $X,Y,Z$ are independent continuous random variables distributed uniformly on $(0,1)$.  I've already derived the pdf of $X+Y$ using the convolution theorem, but there's a line in the answer that says:  $P(Z&gt;X+Y) = \mathbb{E}[\ P(Z&gt;X+Y\ |\  X+Y )\  ]$ where $\mathbb{E}$ is the expectation.  I'm not familiar with this result. Could anyone give a pointer to a similar result if one exists?  Thanks.
Math symbol question: Vertical bar for ''evaluated at ...'' Young boy living on Mars discovers that his parents are robots Mark a comment as the answer to a question I am considering buying a Dell XPS 15 laptop. The laptop has a Nvidia 420m card which should work with Linux but I keep reading that the Nvidia Optimus technology isn't supported on Linux. I am not really interested in switching from Nvidia to Intel to save power but need to know that the Nvidia card will in fact work if I installed Ubuntu.  If anyone has experience using a Nvidia card with Optimus technology or even better the exact laptop in question (Dell XPS 15 with 1GB NVIDIA® GeForce®  GT 420M) it would be great.  A major problem holding people back from adopting Linux is this sort of hardware issue. I am a long term Ubuntu user and supporter who can't afford to make a mistake with a purchase like this. I don't want to spend £500+ to find I have no graphics acceleration because Windows 7 is not an option. By definition a matrix representing a Lorentz transformation is orthogonal, so that its inverse is equal to its transpose.   Consider a pure boost in the t-x plane; $$\Lambda_x=\begin{pmatrix} \cosh(\gamma) &amp;&amp; \sinh(\gamma) &amp;&amp; 0 &amp;&amp; 0\\ \sinh(\gamma) &amp;&amp; \cosh(\gamma) &amp;&amp; 0 &amp;&amp; 0\\ 0 &amp;&amp; 0 &amp;&amp; 1 &amp;&amp; 0\\ 0&amp;&amp;0&amp;&amp;0&amp;&amp;1 \end{pmatrix}.$$ $\Lambda_x$ has inverse  $$\Lambda_x^{-1}=\begin{pmatrix} \cosh(\gamma) &amp;&amp; -\sinh(\gamma) &amp;&amp; 0&amp;&amp;0\\ -\sinh(\gamma) &amp;&amp; \cosh(\gamma) &amp;&amp; 0&amp;&amp;0\\ 0 &amp;&amp; 0 &amp;&amp; 1 &amp;&amp;0\\ 0&amp;&amp;0&amp;&amp;0&amp;&amp;1 \end{pmatrix}$$ but tranpose  $$\Lambda_x^T=\begin{pmatrix} \cosh(\gamma) &amp;&amp; \sinh(\gamma) &amp;&amp; 0&amp;&amp;0\\ \sinh(\gamma) &amp;&amp; \cosh(\gamma) &amp;&amp; 0&amp;&amp;0\\ 0 &amp;&amp; 0 &amp;&amp; 1&amp;&amp;0\\ 0&amp;&amp;0&amp;&amp;0&amp;&amp;1 \end{pmatrix}.$$ These are not equal. Where have I gone wrong? Stability region for two step Nyström method I have the following two step Nyström method: $u_{k+1}=u_{k-1}+2h\cdot f(u_k)$. I want to know the stability region, so I wrote this as $w_{k+1} = A\cdot w_k$ with $A=\left(\begin{matrix} 2h\lambda &amp; 1 \\ 1 &amp; 0\end{matrix}\right)$ and $w_k = (u_{k},u_{k-1})^t$. I use the sample/test equation $u'=\lambda\cdot u = f(u)$ with $\lambda\in\mathbb{C}$. To find the stability region I must set some limitations on the matrix A.  Do I want the whole vector $w_{k+1}$ to go to the zero vector as $k$ goes to infinity, or just the first component that contains $u_{k+1}$? I don't think I can let the second component go to zero, since the matrix just has a $1$ in the bottomleft corner. So I think I want $2h\lambda$ to be negative in the reals (like Forward Euler) , or at least less than 1? I'm unfortunately just guessing at this point.  For (Forward) Euler we have $u_{k+1}=u_k + h\cdot f(u_k) = (1 + h\lambda)u_k$ and so we require that $h\lambda$ does not have a positive real part.  So I guess I also want some anologue for matrices being less than 1? I do not know how to deal with the matrices since the left hand vector not only contains $u_{k+1}$ but also the old $u_k$. How can I make Firefox download different file types to different locations? 98% of what I download is music, so I set the download location to my music folder. However, the other 2% has no place there, so every time I download .doc files or PDF files I have to remove them. Is there a way to make Firefox change the download folder based on file extension? I'll settle for all non-MP3 files getting saved to the desktop.  I know I can right click, choose Save Link As and pick the download location myself, but it seems like there should be a better way. How to prove the midpoint of a chord is also the midpoint of the line segment defined by the points of intersection of other two chords with it? Why can I feel my seven pound cat walking across floor of my home? The house is only 9 years old. (I am the second owner)   I know they settle but in the last year I can feel all movement across the floor- year ago I could barely feel anything but did notice that when someone walked across I could feel them go by.  But more recently the cat walking across to go to the chair I can feel that.  What is going on?  I know I should not feel the cat who is 7 lbs walking by or across the floor. Split level home 9 years old Minnesota location  Is anyone out there that can explain this? CG series about a beast planet Combining two covariance matrices How can I fix a mistake I made on my income tax filing? [US] How can I fix a mistake I made on my income tax filing? Can I convert a string representing a boolean value (e.g., 'true', 'false') into a intrinsic type in JavaScript?  I have a hidden form in HTML that is updated based upon a user's selection within a list. This form contains some fields which represent boolean values and are dynamically populated with an intrinsic boolean value. However, once this value is placed into the hidden input field it becomes a string.  The only way I could find to determine the field's boolean value, once it was converted into a string, was to depend upon the literal value of its string representation.  var myValue = document.myForm.IS_TRUE.value; var isTrueSet = myValue == 'true';   Is there a better way to accomplish this? What is a meta for? A guest at my house over the weekend stood puzzled next to my driveway. &quot;What is that for?&quot; she asked, pointing to a framework of 2x4s and hardware cloth perched on an old tire amid piles of sand. &quot;Sifter.&quot; I said. &quot;For what?&quot; &quot;For sifting gravel.&quot; &quot;Why?&quot; &quot;To line walking paths, such as the one you're standing on...&quot; Spend enough time working with something, and it's easy to forget how strange and unnatural your makeshift tooling can appear to those unfamiliar with it.  Such is the nature of these meta sites. For 5 years, we've been directing folks to them for discussion and feedback, to commune with their community, hash out misunderstandings, propose changes and document the current state of things. And... We haven't always been good about helping them get past the initial shock and confusion of dealing with this system. This has manifested in several unfortunate behaviors:  Downvoting of legitimate support questions - those that are not duplicates and reflect an actual bug or honest misunderstanding of how the system operates. Folks who are acting in good faith should be treated as such - , not shutting them down.  Closing questions that seek input and discussion from the community - in hindsight, adding &quot;primarily opinion based&quot; as a close reason on meta sites was... a terrible idea. The old &quot;not constructive&quot; close reason made some sense for rants and so on, but for a discussion site closing down questions that solicit opinions is just silly. Here on MSE, we prefer the following off-topic reason instead:  This question does not appear to seek input and discussion from the community. If you have encountered a problem on one of our sites, please describe it in detail. See also:    The perception that Stack Exchange is disrupting the normal operation of the site by talking about future plans - even when those plans involve the community. I talked about this a bit more on , but seeing this kind of backlash toward folks at the company who were trying to be open and receptive to discussion about what they were doing was kinda disheartening - we need to be doing more of that, not less.  A reluctance to ask questions about asking questions - which is about as meta as you can get, and yet we probably get more of these via email than we see on meta, while being the least-qualified to answer them well.   After an increasing number of complaints from both core users and moderators on a number of sites, we're taking a hard look at how we can improve this situation... Starting with a change to :  Meta is for...  ...$SiteName users to communicate with each other about $SiteName (asking questions about how the websites work, or about policies and community decisions) ...$SiteName  users to communicate with Stack Exchange the company (posting bugs, suggesting improvements, or proposing new features), and ...Stack Exchange to communicate with the community (soliciting feedback on new ideas or features, or discussing policies that affect the whole network)  Lots of topics are fair game, as long as they are about the Stack Exchange family of Q&amp;A sites in some way. Any issue that concerns the core Stack Exchange engine that runs all Stack Exchange websites is welcome here.  This replaces the previous bullet list of specific topics, and aims to outline broad purposes with examples for clarification rather than constraining the scope to those examples. So... that's a start. But a documentation change isn't going to change misconceptions that've already built up among newer users. So I'm asking y'all for help: What do you think meta should be used for, and how can we better communicate this intent to new users? I have a sheet in which I first apply a filter to a certain column to show "Unique records only". Now I have a column which contains, for e.g., values like:  Applepie Applesauce Crabapple Banana Mango   What I need is the count of all visible cells containing the word "Apple". Note that this should exclude the hidden (filtered out) cells. Now I have found out a formula:  `=SUMPRODUCT(SUBTOTAL(3,OFFSET(Sheet1!A:A,ROW(Sheet1!A:A)-MIN(ROW(Sheet1!A:A)),,1))*(Sheet1!A:A="&lt;Text to search&gt;"))`   However the problem with this one is this formula searches for the entire text. NOT just a part of it. How do I modify this formula to return count of cells containing "Apple" i.e. for this example it should return 3 as the result. I'm consistently receiving significant delays on Stack Overflow when opening the flag dialog on questions. Delays do not occur on any other StackExchange site I have checked. This started a couple days ago (as far as I can tell).  Delays occur not only when loading the initial screen, but also when loading the submenus. This is slightly confusing for a couple seconds (until you're used to it) since it appears as if the flag dialog has simply vanished.   What's going on here? I demand to know, otherwise somebody will be very upset.  Not me. I'm not going to get that upset over something like this.  But someone will.    Specs (though I know of several others who have this issue):  Windows 7 64-bit Chrome Version 30.0.1599.69m     Ping: 31ms Download: 6.88mbps   Upload: 1.07mbps LibVLC.NET in GTK# So I have these two wheels parented to the leg of a robot. I wanna make them spin a few times but they're spinning around the wrong axis. With other objects I could just press R, Y, Y to make them spin right when they're already at an angle, but for some reason it doesn't work with these. Would be amazing if someone helped me fixing this! Are comments discouraged in a BibTeX file? biber complains about "junk" in what should be seen rather as commented-out lines in a BibTeX file.  I was wondering if comments are discouraged in BibTeX at all.  \documentclass {article}  \usepackage {filecontents}  \begin {filecontents} {ref.bib}  @book {book1,  author={author 1},  title={title 1}}   book {book2,  author={author 2},  title={title 2}}   @book {book3,  author={author 3},  title={title 3}} \end{filecontents}  \usepackage [backend=biber] {biblatex} \addbibresource {ref.bib}  \begin {document}   \nocite{*}  \printbibliography \end {document}   Here is biber's output:  INFO - This is Biber 2.1 INFO - Logfile is 'mwe.blg' INFO - Reading 'mwe.bcf' INFO - Using all citekeys in bib section 0 INFO - Processing section 0 INFO - Looking for bibtex format file 'ref.bib' for section 0 INFO - Decoding LaTeX character macros into UTF-8 INFO - Found BibTeX data source 'ref.bib' WARN - BibTeX subsystem: /tmp/No7MbpTruX/ref.bib_31209.utf8, line 13, warning: 43 characters of junk seen at toplevel INFO - Overriding locale 'en-US' defaults 'variable = shifted' with 'variable = non-ignorable' INFO - Overriding locale 'en-US' defaults 'normalization = NFD' with 'normalization = prenormalized' INFO - Sorting list 'nty' of type 'entry' with scheme 'nty' and locale 'en-US' INFO - No sort tailoring available for locale 'en-US' INFO - Writing 'mwe.bbl' with encoding 'ascii' INFO - Output to mwe.bbl INFO - WARNINGS: 1 How do I transfer my Destiny account from Xbox 360 to Xbox One?