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

1. ## 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

2. 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