Math question and answer check
posted by Gayle 52 on .
Consider the probability function. (Give your answers exactly.)
P(x) =
5 − x
10
, for x = 1, 2, 3, 4
(a) Find the mean.
Incorrect: Your answer is incorrect. (my answer was 1).
(b) Find the standard deviation.
(my answer was 1 also on this one. Please help, I just cant get the standard deviation.

You can p(x )
because x values are given
p( x ) = 5x
p(x) = 51 = 4
p(x) = 52 = 3
p(x) = 53 = 2
P(x) = 54 = 1
What about that 10 belong to 
Ok, question is this the way to work this 54/10, 53/10, 52/10, 51/10 or do you divide by 4.

(5x)/10
(51)/10 = 0.4
(52)/10 = 0.3
(53)/10 = 0.2
(54)/10 = 0.1
x 1 2 3 4
P(x) 0.4 0.3 0.2 0.1
It is unclear. What is the 10 doing there 
When you add up all the x's the total is 10 and it is over 10 that is how I came up with the mean of one the first time.

You can check question first
P(x) = (5x)/10 or 5x/10
it is easy to compute mean when you get p(x). 
51/10= 4/10=.4
I do appreciate the patience that you have with me. Am I getting close to it??? 
mean = 1(.4) + 2 (.3) + 3(.2) + 4(.1)
Mean = .4 +.6 + .6 +.4
Mean = 2.0
variance = 1^2 (.4) 2^2(.3) + 3^2(.2) + 4^2(.1)
variance = .4 + 1.2 + 1.8 + 1.6
variance = 5
Standard deviation = sqrt(variance  mean^2)
Sqrt(52^2)) = 1 
Thank you, once I see it worked out I can do others, just done one and got the mean correct so far.

variance = 1^2 (.4) + 2^2(.3) + 3^2(.2) + 4^2(.1