Answer:

And the sample variance can be calculated with this formula:

And the deviation would be:

Step-by-step explanation:
For this case we can calculate the mean with the following table 
Age        Number (f)    Midpoint    x*f                 x^2 *f
25-34         22.1            29.5         651.95         19232.525
35-44         31.5            39.5         1244.25       49147.875
45-54         37.7           49.5         1866.15         92374.425
55-64         25.3           59.5        1505.35        89568.325
Total          116.6                             5267.7        250323.15
And the mean can be calculatd with this formula:

And the sample variance can be calculated with this formula:

And the deviation would be:
