# Thread: Statistics for A2 students

1. ## 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)

2. 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

3. 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.

4. 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.