Can someone check my math for me (Standard Deviation)?

[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)

DUPLICATE POST

http://www.freemathhelp.com/forum/threads/71993-Standard-Deviation-of-a-Frequency-Table