My Math Forum Help!-Variance and Standard Deviation

 Algebra Pre-Algebra and Basic Algebra Math Forum

 February 22nd, 2012, 10:35 AM #1 Newbie   Joined: Feb 2012 Posts: 4 Thanks: 0 Help!-Variance and Standard Deviation Okay, I have a word problem here: Seven Students recorded the marks which they obtained in an intelligence test. Their mean mark was 65 and their standard deviation 10. An eighth student obtained a mark of 65. Calculate the mean and standard deviation of the marks of all eight students. I understand how they get the mean, because it's just [(65*7)+65]/8, which gives you 65- easy enough. But for the standard deviation I keep getting zero! The answer is supposed to be 9.4, could someone please show me how this answer is obtained? I'm clueless! Many thanks in advance!
 February 22nd, 2012, 11:08 AM #3 Newbie   Joined: Feb 2012 Posts: 4 Thanks: 0 Re: Help!-Variance and Standard Deviation Ahh, thank you so much! It makes a lot more sense now, thanks!
February 22nd, 2012, 09:10 PM   #4
Senior Member

Joined: Apr 2011
From: USA

Posts: 782
Thanks: 1

Re: Help!-Variance and Standard Deviation

Quote:
 Originally Posted by daigo Sup bro
Hmm <noting name and picture>

Quote:
 There's probably a whole formula and stuff but I don't remember all of it so this is just the easy way. Maybe someone more skilled can post the more advanced formulaic method, sorry
I don't think there is any special equation for it. I used the same method you did, just simply recognizing that the new student being 65 was adding nothing to our total, and I would guess that was the whole point of the problem.

### calculate the variance and standard deviation of this mark of student

Click on a term to search for related topics.
 Thread Tools Display Modes Linear Mode

 Similar Threads Thread Thread Starter Forum Replies Last Post Kinroh Advanced Statistics 1 September 5th, 2013 12:31 PM HenryMolaison Algebra 2 February 20th, 2013 12:33 PM tsl182forever8 Algebra 2 February 10th, 2012 05:37 AM Axel Algebra 2 April 28th, 2011 03:25 AM 212111 Advanced Statistics 0 August 27th, 2009 01:10 AM

 Contact - Home - Forums - Cryptocurrency Forum - Top