probability question

letsstophere

New Member
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

jerryb

New Member
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

letsstophere

New Member
c)
this is what i did, tell me if i am correct?
0(.1) + 1(.2) + 2(.3) + 3(.2) + 4(.1) + 5(.1)
mean = 2.3

letsstophere

New Member
a)
.1 + .2 + .3 + .2 + .1 = .90
is this correct also?

letsstophere

New Member
d)
is the standard deviation 7.3?

letsstophere

New Member
Yeah im confused on d)
I did this:

0^2(.1) + 1^2(.2) + 2^2(.3) + 3^2(.2) + 4^2(.1) + 5^2(.1)

what did i do wrong??

vinux

Dark Knight
sigma = sqrt( sum {( x-mu)^2*P(x) } ) as jerry mentioned

mu is the mean

letsstophere

New Member
alright i think i got it
0^2(.1) + 1^2(.2) + 2^2(.3) + 3^2(.2) + 4^2(.1) + 5^2(.1)

0+.2+1.2+1.8+1.6+2.5

=7.3 - mean squared 5.29 = 2.01

did i do it?!

letsstophere

New Member
i am terrible at statistics...ugh
back to the drawing board.

letsstophere

New Member
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

letsstophere

New Member
so you are saying...
take the square root of 2.01
which is 1.4177 ...is the standard deviation??

letsstophere

New Member
wanted to let you guys know i got a 100 on this take home quiz. thanks a lot!!