# Homework Help: Binomial Distribution

1. Jan 23, 2012

### planauts

1. The problem statement, all variables and given/known data
http://puu.sh/epl6 [Broken]
http://puu.sh/eplm [Broken]

2. Relevant equations

3. The attempt at a solution
No clue on how to attempt this problem. Any help would be appreciated, thanks!

Last edited by a moderator: May 5, 2017
2. Jan 24, 2012

### Ray Vickson

(a) What is the formula for $f(k) \equiv \Pr\{X = k|X \geq 2 \},$ for k = 2, 3, ...,n? Then $E(X | X \geq 2) = \sum_{k=2}^n k f(k),$ and you ought to be able to get the cited formula from this.
(b) What is the formula for σ in terms of n and p? Look at it carefully.

RGV

Last edited by a moderator: May 5, 2017