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Sir I have the follwong tables, and need to show the Standard Deviation, the formula is also enclosed.

The tables are correct but I am having trouble figuring out the formula, please see below-

3. A company had 80 employees whose salaries are summarized in the frequency distribution below. Find the standard deviation. Find the standard deviation of the data summarized in the given frequency distribution.

Salary Number of Employees

5,001 -10,000 11

10,001 – 15,000 13

15,001 – 20,000 20

20,001 – 25,000 17

25,001 – 30,000 13

salaries frequencies class midpoint X f*x f*x^2

5001-10000 11 7500.5 82505.5 XXXXXXXXX 8

10001-15000 13 12500.5 162506.5 XXXXXXXXXX

15001-20000 20 17500.5 350010 XXXXXXXXXX

20001-25000 17 22500.5 382508.5 XXXXXXXXXX

25001-30000 13 27500.5 357506.5 XXXXXXXXXX

totals 74 (NNN) NNN-NNNNXXXXXXXXXXX

Variance 2 =

x2 f/n – ( xf/n) 2

4. The heights of a group of professional basketball players are summarized in the frequency distribution below. Find the standard deviation.

Height (in.) Frequency

70-71 4

72-73 9

74-75 18

76-77 11

78-79 9

80-81 4

82-83 1

heights frequency class midpoint x f*x f*x^2

70-71 4 70.5 282 19881

72-73 9 72.5 652.5 47306.25

74-75 18 74.5 1341 99904.5

76-77 11 76.5 841.5 64374.75

78-79 9 78.5 706.5 55460.25

80-81 4 80.5 322 25921

82-83 1 82.5 82.5 6806.25

totals 56 4228 319654

Variance 2 =

x2 f/n – ( xf/n) 2