How to calculate variance?

Question

data

classes.....0-1.2-3.4-5.6-7.8-9.

frequency..3-4-8-0-6

from the above data calculate variance

Answer 1

Multiply frequency by the classes midpoints... 0.5 x 3, 1.5 x 4, 2.5 x 8...

Calculate an average (Above answers added together and divided by 5)

Then it is the Sum of each X (midpoint x frequency) minus the average squared!

So: [((0.5x3) - (Average)) squared] + [((1.5x4) - (Average)) squared] Continued all the way to [((8.5x6) - (Average)) squared].

Easy!