# Maths problems - Probablity and Statistics....Never go in my head

• Jul 9th 2009, 12:02 PM
masood
Maths problems - Probablity and Statistics....Never go in my head
Dear All Probablity and Statistics GURUS

I need this help, i have a question for assignment and I really dont kknow how to do that. It might be damn simple, but for me its like breaking the DNA code.

Q1. Find the probablity that 3 heads in 5flips of a balanced coin?
Q2.Find the probablity that LESS THAN 4 heads in 5 flips of a balance coins?

Q3. Find the probablity that MORE THAN 3 heads in 5 flips of a balance coin?

Q4. A production process produces 10 defective items per hour. Find the probablity that 4 or less items are defetive out of the output of randomly chosen hour using
a) The Poisson Distribution and
b) The normal approximation of poisson.

Masood
• Jul 9th 2009, 01:24 PM
CaptainBlack
Quote:

Originally Posted by masood

Q1. Find the probablity that 3 heads in 5flips of a balanced coin?
Q2.Find the probablity that LESS THAN 4 heads in 5 flips of a balance coins?

Q3. Find the probablity that MORE THAN 3 heads in 5 flips of a balance coin?

The probability of $n$ heads in $5$ flips has a binomial distribution $B(5,0.5)$, so:

$p(n\ heads)=b(n;5,0.5)={5 \choose n} 0.5^n (1-0.5)^{5-n}$

Q1: just use the formula above with $n=3$

Q2: let n denote the number of heads, then $p(n \le 4)=1-p(n=5)$

Q3: let n denote the number of heads, then $p(n > 3)=p(4)+p(n=5)$

CB