needing help with this probability problem.......pweeeeze

A school is sending 11 children to a camp. If 25% of the children in the school are first graders, and the children are selected at random, what is the mean and variance of the number of first graders chosen?

Please show us your work - and exactly where you are stuck.

This is again binomial distribution - look up in your text book as to the values of mean and variance for this type of distribution.

When you were given the solution in another of these binomial-type exercises, you replied saying that you "understand totally how to do these now." That's great! Please show your work on this exercise.

Please be complete. Thank you!

Eliz.

Dear Subhotosh Khan,

I don't have a textbook to look out of. I am not starting the class til august 20th. I am just trying to learn for a heads up before the class starts so I am not lost. I am horrible at math and I have to have statistics for my major so I am trying to learn it before going to class.


Dear stapel,

okay i have started out with this:

C(11,4)=(.20)7=0.0000128

But that doesn't sound right, so therefore I am confused.

You are not learning properly through our spoon-feeding.

Doa google search on mean and variance of binomial distribution.

Tell us what you found.

HeatherBelle09 said:

I am horrible at math

Click to expand...

...and PLEASE stop talking like that. Please.

HeatherBelle09 said:

Dear Subhotosh Khan,

I don't have a textbook to look out of. .. I am horrible at math

Click to expand...

Very dangerous idea to teach "yourself" statistics - given the above conditions. You will teach yourself "wrong" concepts/ways - then you'll have to spend time trying to unlearn those.

For example, the work below you have done is so "misguided" - it is not even wrong.

You wrote

C[11,4] = (0.20)7 ....how?

Actually

C[11,4] = (11*10*9*8)/(4*3*2*1) = 330

then

(0.20)^7 = 0.0000128 You forgot very important "^" sign

So I don't know what you were trying to write!

If you feel that you need to get ahead - please get a live tutor and a good book - so that the fundamental concepts are clear.

Good luck...

Dear stapel,

okay i have started out with this:

C(11,4)=(.20)7=0.0000128

But that doesn't sound right, so therefore I am confused.

Click to expand...

If you want a good book for learning stats, get Elementary Statistics by Larson and Farber.

They may be wanting you to use \(\displaystyle np=mean, \;\ npq=variance, \;\ \sqrt{npq}=standard deviation\).

This is used a lot of times when it isn't practical to use the standard form of the binomial probability. Say, when you are using large numbers.