# Thread: Finding mean, variance and standard deviation.

1. ## Finding mean, variance and standard deviation.

If anyone could help me out with the following questions, that would be great!

1. In an exam, 95% of the scores are between 48 and 80. What are the mean and variance of scores?

2. There is a binomial distribution where n=20 and p=10q. What is the mean and standard deviation?

2. ## Re: Probability Question

Originally Posted by gbooker
If anyone could help me out with the following questions, that would be great!

1. In an exam, 95% of the scores are between 48 and 80. What are the mean and variance of scores?
Impossible to answer with out the missing information about what you are to assume about the distribution of marks.

If we assume this is a symmetric 95% interval [48,80] are the mean +/- 1.96 standard deviations. You are expected to know that the standard deviation is the square root of variance.

CB

3. ## Re: Probability Question

Originally Posted by gbooker
2. There is a binomial distribution where n=20 and p=10q. What is the mean and standard deviation?
If $p=10q$ then as $p+q=1$ we have $p=10/11$ and $q=1/11$.

Mean is $np$, and standard deviation is $\sqrt{npq}$
CB