Standard Deviation of a Frequency Table

[I.Hate.Math]

I have to find the mean and Standard Deviation for a frequency table. I've double and triple check my work but it does not seem right. I found the midpoint, the frequency times and midpoint and the frequency times the midpoint squared. Not all colums are shown below.

Table (second column is the frequency)
60-69...12
70-79...14
80-89...11
90-99...1
100-109...1
110-119...0
120-129...1

Here is what I got after filling in the rest of the chart and doing all the work

Mean:76.75

Standard Deviation: 245.5043736 (I think this is wrong but I've done the problem three times and keep getting this)

 

[Deleted member 4993]

I have to find the mean and Standard Deviation for a frequency table. I've double and triple check my work but it does not seem right. I found the midpoint, the frequency times and midpoint and the frequency times the midpoint squared. Not all colums are shown below.

Table (second column is the frequency)
60-69...12
70-79...14
80-89...11
90-99...1
100-109...1
110-119...0
120-129...1

Here is what I got after filling in the rest of the chart and doing all the work

Mean:76.75

Standard Deviation: 245.5043736 (I think this is wrong but I've done the problem three times and keep getting this)

What equations did you use to find the mean (average) and the standard deviation?