P-Chart Standard Error of Proportion

#1
I feel like i'm doing this problem right, but i'm not getting the right answer.

Random Samples of 200 Parts were taken on an assembly line every hour for the past 25 hours. the number of defective parts is shown in the accompanying table:

sample :------1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
# of defective:5 2 4 10 2 6 8 2 0 5 12 11 8 10 5

sample :------16 17 18 19 20 21 22 23 24 25
# of defective:13 7 5 7 11 3 16 3 2 10

What is the estimate of the standard error of the proportion of defective parts?

I used a program to graph the points and found sample 22 out of control. Afterwards i do the calculations of dividing 3sigma by 3 and get a value of 0.012705 but that isn't one of the choices. I used the formula (p*(1-P)) / n too and got the same answer as well. Could it be that i'm using the wrong formula or finding the wrong value?

The options are :

a. 0.0125
b. 0.0251 (i think they have this one listed as correct)
c. 0.0700
d. 0.0002
e. 0.0324
 

vinux

Dark Knight
#2
I think you have calculated the standard error correctly.

But If you use I-MR chart for the proportion instead of P charts, you will get the std err as in b ( 0.0251)