I know that the answer is $\frac{6!}{2!2!}$, but I'm just curious why this is so. I got no intuition for this stuff.
Using all the letters of the word ARRANGEMENT how many different words using all letters at a time can be made such that both A, both E, both R both N occur together .
Identification of fuzzy insect in Pennsylvania I live in south eastern Pennsylvania, USA. About a month ago I came across this very peculiar insect. Its body was about an inch long, it was fuzzy, and it had a long proboscis(?) and long orange legs.  I've been wondering about it ever since. Can anyone identify it? How to do one-class text classification? I have to deal with a text classification problem. A web crawler crawls webpages of a certain domain and for each webpage I want to find out whether it belongs to only one specific class or not. That is, if I call this class Positive, each crawled webpage belongs either to class Positive or to class Non-Positive.  I already have a large training set of webpages for class Positive. But how to create a training set for class Non-Positive which is as representative as possible? I mean, I could basically use each and everything for that class. Can I just collect some arbitrary pages that definitely do not belong to class Positive? I'm sure the performance of a text classification algorithm (I prefer to make use of a Naive Bayes algorithm) highly depends on which webpages I choose for class Non-Positive.  So what shall I do? Can somebody please give me an advice? Thank you very much! Elastic IP address on EC2 instance interface without 1:1 NAT pdflatex, \includegraphics, and multi-page PDF files I have a PDF file with multiple figures; each figure is a separate page in the PDF file.  I am using pdflatex, and I would like to use \includegraphics or equivalent to include some of the figures.  Of course I could use an external tool to split the PDF file into multiple one-page PDF files. Then I could use \includegraphics as usual. However, I would have a much simpler workflow if I could avoid this extra step. Hence the question:  How can I include, e.g., page 3 of foo.pdf as a figure?  I am aware that there is a Latex package called pdfpages, but it seems to be designed for something else: with pdfpages, each page in the input file will produce a full page in the final document, not just a box. setting up apache2 webserver -- differences between behaviour within my intranet and outside Two-Weapon Fighting & Bonus Actions What is the final price if the bid price exceeds the ask price in an order driven market? How to make a water vortex I'm very new to Blender and I'm trying to make a water vortex like this.(may be not the easyest first project for a newbie)     I watched several tutorial on liquids particle etc but I'm not sure what is the best aproach. What I tried  until now:   I made a particle system with a vortex force field. It looks good, but I'm not able to add the right material.      I played around with the fluid physics, the water looks good but if I add a vortex force field it does nothing.   I would be very grateful if somebody could point me in the right direction because I'm definitely stocked. Convert a number to a string with specified length in C++ Missing entry in flagging history I happened to glance upon my flagging history and I realized that there was an entry missing from the spam section in it. I had marked 6 posts as spam, out of which 4 were deemed helpful and 1 was declined. I'm not sure what happened to the remaining 1 entry and why it is missing from the history summary. Here is a snapshot of the spam section of my flagging history.    Is this behavior a  or a ?  Note: I've checked my flagging history completely and there is no spam flag which is still in the active state. I've been reading an  ( eMagazine) relating to the Raspberry Pi; "An ARM GNU/Linux box for $25."  In the article, page 17 at the bottom it shows an area on the Pi where a track zigzags next to a straight one with the explanation text:     The “wiggles” in tracks, ensure signals are matched  electrically,   reducing interference and signal delay.  This is particularly   important for high speed video  data and HDMI signals.     I have very limited knowledge of electrical engineering so perhaps this is a very simple question but why would you incorporate these 'wiggles' in a PCB design?  I realise the quote gives me an answer and I sort of understand the interference point due to problems with power cables and coaxial cables running next to each other but I'd appreciate something assuming very little knowledge that explained why you would get the problems and how wiggles help. For example, why isn't the board covered in wiggles? So a couple of weeks ago my network manager icon stopped appearing; I still get automatically connected to my saved networks and the internet works fine, etc. If I go into System Settings and look at the Network settings I can still see all the networks, only the icon that's normal in the top bar is missing.  I have no idea what caused this, I don't remember installing anything. I think it just happened after a regular update.  I tried these commands to make sure I was properly up-to-date, (which I found on another forum post):  sudo apt-get -f install sudo apt-get update sudo apt-get upgrade   That didn't do it so I found this post:  and I followed the instructions in those answers:  sudo apt-get purge network-manager-gnome &amp;&amp; \ sudo apt-get install network-manager-gnome   And, quoted from an answer there:     Add nm-applet to the Startup Applications (which may be found by   entering "Startup Applications" in the Dash).   I restarted and then saw no Unity interface at all! So I tried those 3 commands above to update again and thankfully that fixed Unity but I still don't have my network manager.  If I try the command nm-applet in a terminal it says:  nm-applet-Message: using fallback from indicator to GtkStatusIcon   So.... I'm pretty much stumped. Any help would be appreciated. I have the following code:  if ($_POST['submit'] == "Next") {     foreach($_POST['info'] as $key =&gt; $value) {         echo $value;     } }   How do I get the foreach function to start from the 2nd key in the array? Textbook on the Geometry of Special Relativity I am looking for a textbook that treats the subject of Special Relativity from a geometric point of view, i.e. a textbook that introduces the theory right from the start in terms of 4-vectors and Minkowski tensors, instead of the more traditional "beginners" approach. Would anyone have a recommendation for such a textbook ?  I already have decent knowledge of the physics and maths of both SR and GR ( including vector and tensor calculus ), but would like to take a step back and expand and broaden my intuition of the geometry underlying SR, as described by 4-vectors and tensors. What I do not need is another "and here is the formula for time dilation..." type of text, of which there are thousands out there, but something much more geometric and in-depth.  Thanks in advance. App Store on Mojave: "We could not complete your purchase. cancelled" Whenever I try to Get then Install any app from the App Store, I get this message:     We could not complete your purchase.  cancelled   I did some searching online, but barely found any useful hits. What is this about?! Find all polynomials $P$ such that $P(x^2+1)=P(x)^2+1$ Find all polynomials $P$ such that   $$P(x^2+1)=P(x)^2+1$$ When I include a  \usepackage{forest} all colored text title, section headings disappears with IEEE Access journal template How can I tackle this problem? Installing Ubuntu 13.04 on a MSATA SSD I am trying to install Ubuntu 13.04 on my 24Gb MSATA SSD. In my laptop, I've also got a 500Gb SATA HDD. I realize that in order for this to work I need to put my /home directory on the 500Gb HDD.   I've tried installing it by creating a ext4 partition on the SSD and a 8Gb swap partition on my HDD. This resulted in an error saying something similar to Cannot install bootloader, please select an other location for the bootloader.   Now before I waste any more time trying to get it to work I'm going to ask a bunch of questions:   Where should I put the swap partition? How big should I make the swap partition? (I've got 12Gb RAM) My 500Gb HDD is currently in Raid mode. Should I change that (to AHCI or IDE)? Where should I put the bootloader if the error message occurs again? How do I make the home directory point to the HDD instead of the SSD? Can I configure Ubuntu to install software/packages on the HDD instead of the SSD? When I ordered this TP-Link AC1300 Wireless Dual Band PCI-Express Adapter (Archer T6E), I looked into customers reviews and they said it worked fine with no drivers on Ubuntu. I didn't have a CD/DVD player on my desktop so I (on a laptop with a DVD drive) copied and pasted the DVD support disk content on to a USB drive and used that. But when I tried to run autorun.exe it puts up archive manager and says An error occurred while loading the archive Ubuntu verison- Ubuntu 16.04 LTS.  Output from: lspci -vnn  02:00.0 Ethernet controller [0200]: Realtek Semiconductor Co., Ltd. RTL8111/8168/8411 PCI Express Gigabit Ethernet Controller [10ec:8168] (rev 11) Subsystem: ASRock Incorporation Motherboard (one of many) [1849:8168] Kernel driver in use: r8169  Kernel modules: r8169   I am fairly new to Ubuntu (1 month) and have learned alot (sudo commands) and now know that windows is overpriced and that ubuntu is better in most fields.  Thanks for the help. Cross Reference problem