Question

CHECK WORK?
X 11 14 16 19 21 23 24 29
P(X) 0.07 0.21 0.17 0.25 0.05 0.04 0.1…
The mean of the discrete random variable X is 18.59.
What is the variance of X? Round your answer to the nearest hundredth.
(I got 31.132)
Var(X) = (11² x 0.07) + (14² x 0.21) + (16² x 0.17) + (19² x 0.25) + (21² x 0.05) + (23² x 0.04) + (24² x 0.1) + (29² x 0.11)
Var(X) = 376.72 - 18.59²

Answer 1

P(X)0.07,0.21,0.17,0.25,0.05,0.04,0.13,0.08

Answer 2

mmm I don't believe that's quite right.

Answer 3

Yea i just seen that..

Answer 4

For each X do:
P(X)(difference from the mean)^2

Answer 5

That is,
P(X)(X-18.59)^2

Answer 6

an then add them up an divide by 8?

Answer 7

Add them up. Don't divide in this case.

Answer 8

When it's equally likely chances, we divide by the number of possibilities.
When each possibility has a different probability of happening, we just multiply each difference by that probability, but we don't have to divide by the number of possibiliities.

Answer 9

Alright,. well I did it, got 267.8929 rounded.... 267.893

Answer 10

Ahhh something is wrong.
Here is what you should have calculated for the first X, X=11:
P(X)*(X-18.59)^2
= 0.07*(11-18.59)^2 = 4.032567

Answer 11

ahh i missed multiplying the P(X)

Answer 12

Important step =)

Answer 13

I hate math... its to time consuming.

Answer 14

It's usually not so bad. But yeah, this kind of problem is tedious. May I suggest using
www.wolframalpha.com?

Answer 15

It's pretty quick and easy to use, can do a lot more than your calculator, and if you make a mistake, you can just go back and edit what you messed up on instead of starting over completely.

Answer 16

Plus, you can copy and paste the link of what you get, and I can look over it and figure out where you went wrong.