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Find Standard Deviation using the computational formula

"My Bank" opens a branchin a commercial district. The bank wants to find out the waiting time of their customers during the Friday evening hours from 5pm to 8pm. Accordingly, the waiting time is recorded for all customers during these hours over a month. A random sample of 20 customers is selected; the waiting time, in minutes, is shown below:
9.50 5.0 8.02 6.00 3.40
8.33 8.35 10.49 5.32 4.08
9.20 5.40 6.17 3.00 2.32
8.35 8.02 6.00 5.15 9.00
Using the data in ungrouped form, compute the Standard Deviation, using the computational formula.

Solution Preview

Please see attached file, but I am including text here just in case. The formula will not appear here.
<br>This is the alternate formula usually used ...