Standard Deviation of a Frequency Table

I.Hate.Math said:

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)

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