Questions About How To Find Standard Deviation Given Mean

Betty asks…

how to find p and q given mean and standard deviation?

Given that a binomial variable has a mean of 12 and a standard deviation of squareroot of 8, find p and n.
I mean , find p and q.

admin answers:

Binomial distribution - mean = np and variance (sd^2) = npq

mean = 12 = np
var = 8 = npq

substituting for np in variance eqn we have


8 = 12q
2/3 = q

since q = 1- p, p = 1/3

12 = n(1/3)
36 = n

Paul asks…

How do I find the percentage of values given standard deviation and mean?

I have a math test tomorrow and can't figure out this question:

The mean and standard deviation of a normal distribution are 150 and 12 respectively. What percentage of values lie between 138 and 162?

Could you please explain how to do this?

Thanks!

admin answers:

In a normal curve, 34% of the cases fall between the mean and -1 standard deviation. Another 34% of the cases fall between the mean and +1 standard deviation. Thus 68% of all cases with between -1 and +1 standard deviation.

Ken asks…

Help! Find mean & Standard Deviation given other variables?

Given that Expected Value = 20,000
P(10,000<=z<=30,000) =.90
Find mean & standard deviation?

I think that the mean = 20,000 but I have no clue how to determine the standard deviation?

admin answers:

I hate standard deviation, I had this Indian instructor trying to explain it in Gen Chem lab. It brings back bad memories! =[

Lizzie asks…

How to find raw score when given the standard deviation and mean?

Find the final exam scores of a class that have a bell shaped distribution with a mean of 65 and a standard deviation of 11....


B) between what scores 95 percentage of the exames are covereD?

e) what scores of the exam are considered outliers??

admin answers:

B) 95% of the scores are within two standard deviations of the mean. This means that if you take 65-11-11 that will give you the low score (which is 43) and if you take 65+11+11 that will give you the high score (which is 87) So, 95% of the scores should be between 43 and 87.

E) Outliers would be scores beyond three standard deviations of the mean. On the low end that would be scores below 65-11-11-11 which would be 32. On the high end that would be scores above 65+11+11+11 which would be 98. So, scores below 32 and scores above 98 would be outliers.

Joseph asks…

How do you find the mean if given Standard deviation? Please look at the question!!?

Please help:

The number of accidents occuring at a given location in a month is unknown to conform Poisson Distribution. The Standard deviation of this distribution is 2 accidents per month.
What is the probability that no accidents will occur during this month?
I just need to find out the mean, so I can do the rest with my own calculator.
please help me i have exam tmw.
Thank you

admin answers:

For a poisson distribution,

the variance = mean λ, so

2^2 = λ

λ = 4
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