# Math Help - mean & standard deviation -- been stuck for days

1. ## mean & standard deviation -- been stuck for days

A random sample of 50 new mothers was asked to estimate how much they spent on prenatal care. The results are present in the frequency distribution presented below.

Amount spent on prenantal Care ($) Mothers (Number) 0-99 2 100-199 4 200-299 8 300-399 20 400-499 16 Total 50 Calculate the mean amount spent on prenatal care AND using the short cut formula to calculate the standard deviation of the amounts spent on prenatal care. I got 229.5 for the mean but Im not sure if this is right, and the numbers im getting for standard deviation are all over the place. any help would be really appreciated. thanks 2. ## Re: mean & standard deviation -- been stuck for days Originally Posted by rensmom A random sample of 50 new mothers was asked to estimate how much they spent on prenatal care. The results are present in the frequency distribution presented below. Amount spent on prenantal Care ($) Mothers (Number)
0-99 2
100-199 4
200-299 8
300-399 20
400-499 16

Total 50

Calculate the mean amount spent on prenatal care AND using the short cut formula to calculate the standard deviation of the amounts spent on prenatal care.

I got 229.5 for the mean but Im not sure if this is right, and the numbers im getting for standard deviation are all over the place.
any help would be really appreciated. thanks
from what ive learned, you just have to use the midpoint of each class.
so your data will be as follows:
49.5; 2
149.5; 4
249.5; 8
349.5; 20
449.5;16

use that to find the mean and sd