Help in statistics please

Hello, I was wondering of someone could help me with questions number four please.. Many thanks

15 women who received HRT treatment provided data on bone density at both
the start of the treatment and at 24 months. We are told that ∑x was 20.37
and ∑x2 was 38.23 for BMD at 24 months in this group.
Q3) What is the mean BMD in the HRT group?
a. 1.36 g/m2
b. 2.55 g/m2
c. 5.26 g/m2
d. 9.87 g/m2
e. 0.53 g/m2
Q4) What is the variance in BMD in the HRT group?
a. 0.75
b. 0.046
c. 0.70
d. – 19.09
e. 1.28

Reply 1

mqb2766

Original post by Dani69

There are two common formulae for variance, you should have come across one that looks something like
E(x^2) - (E(x))^2
so the mean of x^2 minus the square of the mean of x. Youre given most of it because you have the sum of x^2 and youve worked out the mean of x in 3).