STATISTIC(STANDARD DEVIATION, PLS HELP)

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The production of batteries manufacturing department of a company is monitored weekly.100 such batteries have to be produced each week before being tested by putting them into toys and seeing how long they last.The results of 20 tests are shown below:
31 42 50 25 29
40 36 24 29 30
40 46 38 34 26
24 22 39 40 21

In this question, i had to use stem and leaf method..and using box and whiskers.
For median, i got10.5 which is 32.5
lower quartile, i got23.5 and upper quartile, i got 15 +16/2 which is 40..

for mean which is EFM/EF which is 668/20 = 33.4
(the answers are correct..and has
already been corrected)
In this question, u have to draw the distribtution table..

MY problem is how you calculate the standard deviation????

PS: I know its formula..but i dnt get the right answer which is supposed to be 8.33
I would be very grateful if somework can help me in that part...in details????

  • STATISTIC(STANDARD DEVIATION, PLS HELP) -

    mean = 33.3

    differences:
    -2.3,8.7,16.7,-8.3,-4.3,6.7,2.7,-9.3,-4.3,-3.3,6.7,12.7,4.7,0.7,-7.3,-9.3,-11.3,5.7,6.7,-12.3

    squares:
    5.29,75.69,278.89,68.89,18.49,44.89,7.29,86.49,18.49,10.89,44.89,161.29,22.09,0.49,53.29,86.49,127.69,32.49,44.89,151.29

    sum of squares: 1340.2
    divide by n-1: 70.54 <-- variance
    take root: 8.40

    Done it by hand, and several online calculators. Can't get 8.33

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