probability question

#1
Hello,
I am having trouble with my stat homework. Maybe someone can give me some guidance? I would really appreciate it!

A woman is fishing for bass on Pinelands pond. Let x=number of 'keepers' that she catches in an hour. The probability distribution for x is given in the table below

x= 0 1 2 3 4 5
p(x)= .1 .2 .3 .2 .1 .1


Questions:
a) What is the probability that she catches at most 4 keepers?
b) What is the probability that x is greater to and equal to 3?

c) Find Ux, the mean number of keepers caught
d) Find the standard deviation for X, the number of keepers caught
 
#2
a) the probability of at most 4 is equal to the probability of three or fewer. simply add up the probabilities involved.

b) use the above and adjust for three or greater

some examples:

c) for a probability distribution x= 2 4 6 8 10, P(x)= .1 .3 .1 .2 .3 Ux + 2(.1)+4(.3)+6(.1)+8(.2)+10(.3) = 6.6

d) sigma = sqrt( sum(x-mu)^2*P(x)) so, to begin the pattern for my example in c) = sqrt((2-6.6)^2(.1) + (4-6.6)^2(.3)...)=2.83
 
#13
okay i calculated it again but came out to 2.01!!! which is the variance.
if i squared the variance (2.01)^2 = 4.0401
would that be the standard deviation??
thanks