   SEARCH HOME Math Central Quandaries & Queries  Question from Pat, a parent: I have looked over your math question and mines is not there. for a binomiial distribution with parmeter n and p, the mean is np and the standard deviation is np(1-p). I understand how to get the np but not understanding how to get the (1-p). For example np=(40)(0.48)(1-0.48)=3.160. How can I get the (1-0.48) answer please Hi Pat,

The standard deviation is actually the square root of np(1-p). In this example p = 0.48 so 1 - p = 1 - 0.48 = 0.42

I hope this helps,
Harley

Pat wrote back

Sorry, but that tdid not help.
the problem answer is as follows np=(40)(0.48)=19.2. I understand that multiply this.
than they did a standard deviation of the distribution of the number, a sign that looks like a square root but it is not so under this sign it sys np(1-p)=that same sign (40)(0.48)(1-0.48~3.160 I do not understand how they got 3.160. please help. I am 55 years and in school and this is hurting me. thank you for your help. Also is there somewhere on the internet where I can download the different math symbols?

Pat,

From what you are describing you see

√(40)(0.48)(1-0.48)

What this means is calculate

(40)(0.48)(1-0.48)
= (40)(0.48)(0.52)
= 9.984

Then te symbol √ says to take the square root so

√9.984 = 3.159746

Does this help?
Harley     Math Central is supported by the University of Regina and The Pacific Institute for the Mathematical Sciences.