How do I find the 1.5 standard deviations BELOW the mean for this problem??

Question

If you could help explain this to me that would be great, thank you

 

A sample of 100 clients of an exercise facility was selected. Let X = the number of days per week that a randomly selected client uses the exercise facility.

X Frequency

0	2
1	13
2	31
3	29
4	11
5	7
6	7

I need help finding the number that is 1.5 standard deviations BELOW the mean (I need to round the answer to three decimal places).

Answer 1

X Freq Subtotal Subtotal X^2

0 2 0 0

1 13 13 13

2 31 62 124

3 29 87 261

4 11 44 176

5 7 35 175

6 7 42 252

--------------------------------------

100 283 1001

Mean Avg = 283/100 = 2.83

variance = (subtotal x^2 - 100* mean^2)/99 = 2.021313131

stnd dev = sqrt(variance) = 1.421728923

mean - 1.5*stnd dev = 0.697406615