# Thread: I need some help

1. ## I need some help

I am having trouble getting the mean and standeard deviation. could you please show me how ? thanks

perscription data
0.4-1.1
1.2-1.9
2.0-2.7
2,8-3.5
3.6-4.3
Frequency
2
2
4
3
9

2. whats wrong?

the mean is the sum of the mid points of each class times the class frequency divided by the total frequency

and then the standard deviation is $\sqrt { \frac { \sum{fx^2}}{\sum{f}} - \mu^2 }$

its just a simple formula where are you having trouble ?

3. how do i get the class mid points ?

4. take the mean of the upper and lower boundaries.

for example $\frac{0.4 + 1.1}{2}$