# [SOLVED] Finding Standard Deviation

• May 18th 2009, 09:43 AM
Lovely07
[SOLVED] Finding Standard Deviation
Q: A company manufactures batteries in batches of 21 and there is a 3% rate of defects. Find the standard deviation for the number of defects per batch.
A: 0.782

I know how to find standard deviation when given a list of data but how can I find it when just given the information above?
• May 18th 2009, 02:51 PM
pickslides
$\sigma = \sqrt{np(1-p)}$

in your case $n = 21$ and $p = \frac{3}{100}$

give it a shoot!
• May 18th 2009, 05:09 PM
Lovely07
^ Thank you for the help it worked. =)