# Statistics for A2 students

• Jan 18th 2010, 09:59 AM
teju
Statistics for A2 students
hi there, im stuck on this question:
x 1 2 3 4
P(X=x) 0.1 0.2 0.4 0.3

the table shows the distribution of the discrete random variable X, find
(a) Var(X)
(b) Var(X^2)
(c) Var(24x^-1)

• Jan 18th 2010, 10:01 AM
artvandalay11
do you know the formula for variance? and its easier counter part in terms of expected value... use that

then you need a theorem about variance when it comes to constants and random variables... are you familiar with that
• Jan 18th 2010, 10:11 AM
teju
Quote:

Originally Posted by artvandalay11
do you know the formula for variance? and its easier counter part in terms of expected value... use that

then you need a theorem about variance when it comes to constants and random variables... are you familiar with that

yh i know the formula for variance its E(x^2) - (E(X))^2, im not familiar with constants and random variables yet, im working on it. is it possible you can show the working out for the second and third part, as i can do the first part.
• Jan 18th 2010, 02:30 PM
mr fantastic
Quote:

Originally Posted by teju
yh i know the formula for variance its E(x^2) - (E(X))^2, im not familiar with constants and random variables yet, im working on it. is it possible you can show the working out for the second and third part, as i can do the first part.

Construct a probability table for Y = X^2:

y 1 4 9 16
P(Y=y) 0.1 0.2 0.4 0.3

Now calculate Var(Y) just just like you calculated Var(X) in the first part.

Construct a probability table for W = 24x^-1 and calculate Var(W) just like you calculated Var(X) in the first part.