In: Statistics and Probability
Jan | 523.9 |
Feb | 510.23 |
March | 545.65 |
April | 514.23 |
May | 550.71 |
June | 505.34 |
July | 525.34 |
August | 600 |
Sept. | 569.42 |
October | 500.2 |
Novem. | 533.12 |
December |
507.11 |
What percentage of your bills are within two standard deviations of the mean?
The answer is:
First, we calculate the mean, standard deviation. Then we calculate the upper and lower limits of the 2 SD of the mean as shown below:
Mean | 532.1041667 |
SD | 29.85258675 |
Mean - 2*SD | 472.40 |
Mean + 2*SD | 591.81 |
Then test whether individual values are within this interval or not:
Month | Amount | Is between Mean - 2*SD and Mean + 2*SD |
Jan | 523.9 | TRUE |
Feb | 510.23 | TRUE |
Mar | 545.65 | TRUE |
Apr | 514.23 | TRUE |
May | 550.71 | TRUE |
Jun | 505.34 | TRUE |
Jul | 525.34 | TRUE |
Aug | 600 | FALSE |
Sep | 569.42 | TRUE |
Oct | 500.2 | TRUE |
Nov | 533.12 | TRUE |
Dec | 507.11 | TRUE |
Then ratio is simply 11/12
Using excel to answer the same:
Calulations:
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