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.

Math question and answer check 
Kuai,
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 
Math question and answer check 
Gayle 52,
Ok, question is this the way to work this 54/10, 53/10, 52/10, 51/10 or do you divide by 4.

Math question and answer check 
Kuai,
(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 
Math question and answer check 
Gayle 52,
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.

Math question and answer check 
Kuai,
You can check question first
P(x) = (5x)/10 or 5x/10
it is easy to compute mean when you get p(x). 
Math question and answer check 
Gayle 52,
51/10= 4/10=.4
I do appreciate the patience that you have with me. Am I getting close to it??? 
Math question and answer check 
Kuai,
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 
Math question and answer check 
Gayle 52,
Thank you, once I see it worked out I can do others, just done one and got the mean correct so far.

Math question and answer check 
Kuai,
variance = 1^2 (.4) + 2^2(.3) + 3^2(.2) + 4^2(.1