apt-get update updates all the packages?
What does "sudo apt-get update" do?
How can adding a 2nd IV make the 1st IV significant? I have what is probably a simple question, but it is baffling me right now, so I am hoping you can help me out.  I have a least squares regression model, with one independent variable and one dependent variable. The relationship is not significant. Now I add a second independent variable. Now the relationship between the first independent variable and the dependent variable becomes significant.  How does this work? This is probably demonstrating some issue with my understanding, but to me, but I do not see how adding this second independent variable can make the first significant. How to prevent non-alphanumeric input in javascript? Transfer Clash of Clans account from one G+ to another G+ account? Is it possible to skip releases during an upgrade? What does "xmlns" in XML mean? Windows Spotlight Source and Save locations? Where are the images from  coming from?  Where are they being saved on my system?  Is there any way for me to point this at my own source of images? Permutation count of AABBC Given a string:  $AABBC=A^2B^2C^1$   I am trying to find the Total Permutations (this may be incorrect):  $\dfrac{5!}{2!\cdot2!}=30$  My question is how would I find the partial sums (perhaps the wrong choice in words) when added together would give an index such that:   $AABBC=1$ $ABABC=2$ $CBABA=29$ $CBBAA=30$   (30 might be the wrong number here but is suppose to be the last)   I have tried to draw out a tree structure to get an idea and thought with as the minimum:  $CAABB$  $4(\dfrac{4!}{2!\cdot2!})$ + 1  And:  $CABAB$  I would get something like:  $4(\dfrac{4!}{2!\cdot2!}) + 0 + 1(\dfrac{2!}{2!}) + 0 + 0$  But I am missing something here. How would I find the sums needed for $BACAB$ ?  More specifically I am trying to find the index of a word that is arbitrarily long in alphanumeric.  So the string may also be something like:  $AAAAABBBBDDEEFFFGGGGGHIIIIJJJJKLMOOOPZZZZZ$ I'm trying to generate a secret key to be used for HMAC SHA-256 signature processing. I've seen many sample of keys with variable length from 32 characters to 96 characters.  What is the ironclad rule for this key size? How can one prove that $\lim_{n \to \infty}a^{1/n}=1$ for every $a>0$? Prove that $\lim_{n \to \infty} a^{\frac{1}{n}} = 1$ if $a &gt;0$.  In my textbook, we are given a suggestion to let $a^{\frac{1}{n}} = (1+h_n)$ and then show that the $h_n$ term goes to zero using a Theorem that states the following conditions:  $\lim_{n \to \infty} = \infty,$ if $a &gt;1, 1,$ if $a = 1,$ and 0, if $\vert a \vert &lt; 1$. I apologize for not formatting the above cases appropriately; I could not figure out how to use a giant left brace to group them altogether.  If I rewrite it as $a^{n^{-1}}$, then I thought that this might help, but I don't think the Binomial Theorem would then apply since the exponent is negative. Furthermore, the problem is only concerned with the positive, real $n$-th roots. I am quite stuck on this problem and any suggestions or advice would be greatly appreciated.   I am using the textbook Introduction to Analysis by Arthur Mattuck. MapThread with non-rectangular lists What is the distinction between a professional and amateur photographer? Why can I put an electrolytic capacitor on AC? I have seen here and there schematics with electrolytic capacitors put on AC. And this sounds weird to me.  Electrolytic capacitors have a polarity, right? If we invert the polarities on DC, bad things happen. As far as I understand, AC inverts polarity every now and then (commonly 50Hz). Why can we put such capacitors on AC without damaging them?  Example:    from demonstration here: Fantasy piece involving different worlds and a crippled protagonist This is a novel that I think I remember reading somewhere in the 1990s courtesy of my brother (who does not remember the book). Only a few details are coming to mind at the moment. It's a male protagonist. Something was not quite right with his legs, which led to him being nicknamed Frog or Leapfrog due to his usual method of locomotion, which consisted of pushing off from his legs to his hands and vice versa. Something happens and he winds up moving between a number of worlds (I want to say that he fell into a well or a hole in a field). There was a part which stuck with me where he's in a bottomless hole and finds he keeps falling faster and faster without end with the rushing wind becoming actively painful (I don't remember if he actually reaches a terminal velocity or if some aspect of the world prevented it while still allowing the rushing air to affect him physically).  Unfortunately, that's all I can remember. I don't remember whether he eventually gains companions on the voyage or how it ended. The most vivid memory is that of the nonstop falling. The AC adapter supplied with my laptop is designed to accept voltage in the range of 100-240VAC at 50-60Hz, but the AC cable that plugs into the adapter unit itself is only rated to 125VAC 7.5A 2.5A.  I know the adapter can accept 220V power, but is it safe to use this cable with the AC adapter to plug into a 220V socket?  Edit: The part in question is a 90W HP Smart AC Adapter.  The laptop does not cause the AC adapter to draw more than about 80 watts from the socket (as measured with a Kill A Watt meter).  Edit 2: The amperage rating of the cable as marked on the attached label is 2.5A, not 7.5A. Correlations with unordered categorical variables I have a dataframe with many observations and many variables. Some of them are categorical (unordered) and the others are numerical.  I'm looking for associations between these variables. I've been able to compute correlation for numerical variables (Spearman's correlation) but :   I don't know how to measure correlation between unordered categorical variables. I don't know how to measure correlation between unordered categorical variables and numerical variables.   Does anyone know how this could be done? If so, are there R functions implementing these methods? Asking a question: DO or ARE? When should you ask a question with &quot;do&quot;, and when with &quot;are&quot;?  In other words,  Are you going to Spain next week?   Do you like Chinese food?  What is the rule here?  We don't say  Do you go to Spain next week?   Are you liking Chinese food?  Why is that? Automatic text wrapping in ArcMap layout text element? How to execute consecutive commands from history? Suppose I want to execute a sequence of four commands that I have executed before. If the first one is 432 in the command-history, then I could do:  $ !432; !433; !434; !435   I'm curious, is there a more efficient way to accomplish this? After reading a couple of answers and comments on some SQL questions here, and also hearing that a friend of mine works at a place which has a policy which bans them, I'm wondering if there's anything wrong with using backticks around field names in MySQL.  That is:  SELECT `id`, `name`, `anotherfield` ... -- vs -- SELECT id, name, anotherfield ... Is it mandatory to have a link to the theme designer? I just wanted to know if it's ok to modify/remove links pointing to the designer of the theme.  In my case I have "theme by" and the site's logotype, would it be ok to remove the logotype and write the site's name? Or remove it altoghether?  Does it have to do with the particular designer of the theme?  Thanks