# Finding two unknowns from varience and mean

1. Nov 18, 2007

### resresd

the data given below are from a discrete distribution with positive integer values.there are two values which are unknown, namely "a" and "b".

8,5,3,6,5,9,a,b

if the mean and varience respectively are 6.5 and 7.75, what are the possible values of "a" and "b"?

so far i have that a+b=16 since 3+5+5+6+8+9+a+b/8=6.5 and 6.5x8=64
3+5+5+6+8+9=36 and 64-36=16

i know that the square root of 7.75=2.783882...=standard deviation,but i don't know what to do with this information in order to find a and b

2. Nov 18, 2007

### EnumaElish

How do you obtain variance from a set of data?

3. Nov 18, 2007

### rock.freak667

well you know that $\sigma=\sqrt{var(x)}$ and you know var(x)...how do you find standard deviation from the set of data given?