remy Posted April 22, 2009 Report Share Posted April 22, 2009 (edited) HiThey ask me to calculate the mean and standard deviation using the gdc of t:Time | nr of people0 <(equal) t < 15 | 2115 <(equal) t < 30 | 32...and so on <(equal) just means greater or equal toI tried to calculate the mean by taking the midpoint, but the result is incorrect. So I guess it is maybe because it is "greater or equal to" and not just simple "0-15"...Can anyone help me out please? Thanks.(Edit: coz I misunderstood the question) Edited April 22, 2009 by remy Reply Link to post Share on other sites More sharing options...
Mike Posted April 22, 2009 Report Share Posted April 22, 2009 Can you post the whole question? Reply Link to post Share on other sites More sharing options...
remy Posted April 22, 2009 Author Report Share Posted April 22, 2009 Of course, its from the November 07 paper 2:Time spent per day (t minutes); number of people0 ≤ t < 15; 2115 ≤ t < 30; 3230 ≤ t < 45; 3545 ≤ t < 60; 4160 ≤ t < 75; 2775 ≤ t < 90; 11Question: Use your graphic calculator to calculate approximate values of the mean and standard deviation of the time spent per day one these mobile phones.The answer: mean = 42.4, standard dev. = 21.6 Reply Link to post Share on other sites More sharing options...
Ongfufu Posted April 23, 2009 Report Share Posted April 23, 2009 Of course, its from the November 07 paper 2:Time spent per day (t minutes); number of people0 ≤ t < 15; 2115 ≤ t < 30; 3230 ≤ t < 45; 3545 ≤ t < 60; 4160 ≤ t < 75; 2775 ≤ t < 90; 11Question: Use your graphic calculator to calculate approximate values of the mean and standard deviation of the time spent per day one these mobile phones.The answer: mean = 42.4, standard dev. = 21.6This shows a continuous random variable. Rather than a probability distribution, continuous random variables have probability density functions. Since a function is not given, we have to convert this distribution into a discrete random variable distribution. This is done by choosing the midpoint of each range of "time spent per day", as X.The formula for mean and SD for a discrete random variable distribution are .For mean, plug the midpoints (7.5, 22.5, 37.5...) as x, and the # of people as p(x). The sum of each is about 42.35.For SD, plug the same values as x and p(x), and use the sum to subtract mean squared, and square root the answer. It should be 21.6. 1 Reply Link to post Share on other sites More sharing options...
remy Posted April 23, 2009 Author Report Share Posted April 23, 2009 Thanks, I also figured out how to make the calculator consider both columns in the statistics program. Reply Link to post Share on other sites More sharing options...
deissi Posted April 23, 2009 Report Share Posted April 23, 2009 For those still in need of assistance with the calc, for TI the command is1-Var Stats L1,L2Where L1 and L2 are the lists containing the midpoints and respective frequencies. Reply Link to post Share on other sites More sharing options...
lois lee Posted February 28, 2010 Report Share Posted February 28, 2010 [quote name='remy' date='Apr 23, 2009 - 08:19' timestamp='1240474770' post='44068'] Thanks, I also figured out how to make the calculator consider both columns in the statistics program. [/quote] [font="Book Antiqua"]how did you do that??? thanks [/font][color="#483D8B"][/color] Reply Link to post Share on other sites More sharing options...
PeacefulChaos Posted March 18, 2010 Report Share Posted March 18, 2010 [quote name='lois lee' date='Feb 28, 2010 - 09:37' timestamp='1267349848' post='63942'] [quote name='remy' date='Apr 23, 2009 - 08:19' timestamp='1240474770' post='44068'] Thanks, I also figured out how to make the calculator consider both columns in the statistics program. [/quote] [font="Book Antiqua"]how did you do that??? thanks [/font][color="#483D8B"][/color] [/quote] Plug in the midpoints for L1. Plug in the frequencies for L2. Then go to STAT -> CALC -> 1-Var Stats then type L1,L2 -> ENTER Reply Link to post Share on other sites More sharing options...
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