plainlazy84 Posted May 23, 2005 Report Share Posted May 23, 2005 I have a statistics exam tommorow, and this is my weakest subject by miles :) can anyone shed any light on how you find Standard deviation using a Casio (FX-85ms) calculator? I dont have the steps for how to do it the quick way by calculator in my notes! If you can help then i will sing your praises. Thanks anyone that can help! edit here is a little question that could be used as an example. A small business which employs only fine staff pays the following salaries 6, 10, 8, 12, 8 (£000) find the variance and standard deviation Quote Link to comment Share on other sites More sharing options...
Burton Posted May 23, 2005 Report Share Posted May 23, 2005 its all the numbers squared minus the square of the mean divided by how may numbers(not including the mean) square rooted...... is not over the mean squared.... Quote Link to comment Share on other sites More sharing options...
Sameer Posted May 23, 2005 Report Share Posted May 23, 2005 Man, I hate S1 so damn much! I'm sitting it for, like, the third time in June. :) Quote Link to comment Share on other sites More sharing options...
somberlaine Posted May 23, 2005 Report Share Posted May 23, 2005 find the mean value (in this case 8.8) then take every number in your number set and take the mean away from the number. then square this number. i.e. (6-8.8)^2 + (10-8.8)^2 + (8-8.8)^2 + (12-8.8)^2 + (8-8.8)^2. once you have added up all these values, divide by the number of data in your set (in this case you will be dividing by 5) this value is the variance. to get the standard deviation, simply square root the variance. hope that helps.... Quote Link to comment Share on other sites More sharing options...
Tomm Posted May 24, 2005 Report Share Posted May 24, 2005 Nah, you can do it all automatically in the calculator. I presume your calculator has similar buttons to mine which is a Fx-85WA. Anyway. Press the mode button, then 2 (SD) to enter SD mode. To make sure there's nothing in the memory already, press shift and then AC (Although on yours it looks like it might be shift and mode). Press equals to clear the memory. Now add numbers one at a time by pressing the number, followed by M+ When you're done adding numbers in, you can choose one of the options that should be printed on the card that's on the inside of the calculator case. On mine, you press Alpha then A for the Sum (x^2) Alpha then B for the Sum x Alpha then C for n etc For SD it's shift then 2 (looks like xQn) All this should be on the reference card for the calculator. Dunno what functions your calculator has though. Should be able to do it. Mine does stuff way more complicated than that, so I would have thought you'd need a pretty crap calculator to not do SD :) Quote Link to comment Share on other sites More sharing options...
scott-mad Posted May 24, 2005 Report Share Posted May 24, 2005 i love you people ive learnt more about sd in 5 mins on a trials forum than in maths! (Y) Quote Link to comment Share on other sites More sharing options...
plainlazy84 Posted May 24, 2005 Author Report Share Posted May 24, 2005 thanks guys youve all been a big help. Looking much better for the exam now (Y) i appreciate your maths skills :D Quote Link to comment Share on other sites More sharing options...
plainlazy84 Posted May 24, 2005 Author Report Share Posted May 24, 2005 right this is annoying :D my book seems to have a slighltly different way of calculating the S.D (it did have how to do it the long way but not how to quickly on calc) basically the same as what somberlaine said but divide by n-1 not n i think this has something to do with whether the group of data is from a population or sample. anyway thats fine and i can work it out by hand. But aimed at Tomm especially- dont suppose there is anyway to change the quick calculation method to allow for this? basically your way is very good but it allows for divided by n and not n-1 and i get a slightly different answer (Y) thanks for any help Quote Link to comment Share on other sites More sharing options...
Tomm Posted May 24, 2005 Report Share Posted May 24, 2005 Well on my calculator there is a button for xQn-1. I think you're right - you do use that for population samples. I might be well off though, my memory of these things is pretty hazy. Try Shift + 3. That's what it is on mine (Y) EDIT: Actually I dunno now. Check when you're supposed to use xQn and xQn-1, because I'm not sure at all. Either way though you should be able to use the calculator :D Quote Link to comment Share on other sites More sharing options...
plainlazy84 Posted May 24, 2005 Author Report Share Posted May 24, 2005 How blindingly obviouis was that! (just use the xQn-1 button instead of xQn (Y) ) you sir are a legend! cheers for the help, finger x for the exam now. thanks again you helpful bean :D Quote Link to comment Share on other sites More sharing options...
Burton Posted May 24, 2005 Report Share Posted May 24, 2005 How blindingly obviouis was that! (just use the xQn-1 button instead of xQn (Y) ) you sir are a legend! cheers for the help, finger x for the exam now. thanks again you helpful bean :D ← But remember to show your workings out!!! Quote Link to comment Share on other sites More sharing options...
plainlazy84 Posted May 24, 2005 Author Report Share Posted May 24, 2005 dont worry i wont forget to- dont want to be losing marks. cheers Quote Link to comment Share on other sites More sharing options...
Tomm Posted May 24, 2005 Report Share Posted May 24, 2005 No problem. If it's stats S1, you can get all the marks by simply writing down n, the mean, sum x squares etc. All of which you can just get off the calculator (Y) Quote Link to comment Share on other sites More sharing options...
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