Posted by Allen on .
Here's a frequency distribution table for the speeds of a sample of automobiles.
Speed(MPH) Frequency Midpoint(I found)
5054 2 52
5559 4 57
6064 5 62
6569 10 67
7074 9 72
7579 5 77
I am trying to find the variance but whatever I do I can't seem to find the answer.
The choices are
c.48.570
d.50.00

Math 
PsyDAG,
Using the midpoints of each interval, to find the mean first = sum of scores/number of scores.
Subtract each of the scores from the mean and square each difference. Find the sum of these squares. Divide that by the number of scores to get variance.