# Need Urgent Help!!!!!!!!!

• Jul 1st 2008, 06:52 AM
fk36@le.ac.uk
Need Urgent Help!!!!!!!!!
Can anyone help me with the following problem asap:

There are 9 tennis balls in a box, of which only 5 have not previously been used. Four of the balls are randomly chosen from the box. Let 'z' be the number of new balls among the selected ones:
(a) Find the probability Distribution of z
(b) Evaluate the expectation E(z)
(c) Evaluate the variance Var(z)

Cheers Guys!!!
• Jul 1st 2008, 02:48 PM
mr fantastic
Quote:

Originally Posted by fk36@le.ac.uk
Can anyone help me with the following problem asap:

There are 9 tennis balls in a box, of which only 5 have not previously been used. Four of the balls are randomly chosen from the box. Let 'z' be the number of new balls among the selected ones:
(a) Find the probability Distribution of z
(b) Evaluate the expectation E(z)
(c) Evaluate the variance Var(z)

Cheers Guys!!!

Read up on the hypergeometric distribution: Hypergeometric distribution - Wikipedia, the free encyclopedia