# Homework Help: Do I perform a Z-test?

1. Feb 4, 2008

### aptiva

Hi all:

1. The problem statement, all variables and given/known data

Sample 1: M = 62.77, SD = 6.52
Sample 2: M = 72.91, SD = 6.22
Sample 3: M = 74.61, SD = 6.60

2. Relevant equations

Now if I wanted to calculate what proportion of students in each population would be expected to receive a grade <50 and receive a grade >80, would I perform a Z-test using Z = (X-mu)/Sd

3. The attempt at a solution

For example, in sample 1:

(For <50)
Z = 50 - 62.77 / 6.52 = -1.959, P = 0.0202 (according to Z-table)
So, .5 - .0202 = .4798 = approximately 48% of the students in the first population would receive a score <50...is that correct?

(For >80)
Z = 80 - 62.77 / 6.52 = 2.65, P = 0.4965(according to Z-table)
So, .5 - .4965 = .0035 = approximately .35% of the students in the first population would receive a score >80...?
1. The problem statement, all variables and given/known data

2. Relevant equations

3. The attempt at a solution