# Probability ???

• Oct 6th 2008, 03:14 AM
Sameera
Probability ???
Probabaility that a pen manufactured by a company will be defective is 1/10.If 12 such pen are manufacturd,find yhe probability for?

1. exactly two will be defective
2. at least two will be defective
3.none will be defective

THANKS !!!!!!
• Oct 6th 2008, 03:55 AM
mr fantastic
Quote:

Originally Posted by Sameera
Probabaility that a pen manufactured by a company will be defective is 1/10.If 12 such pen are manufacturd,find yhe probability for?

1. exactly two will be defective
2. at least two will be defective
3.none will be defective

THANKS !!!!!!

Are you familiar with the binomial distribution?

Let X be the random variable number of manufactured pens that are defective.

X ~ Binomial(n = 12, p = 1/10).

Calculate:

1. $\displaystyle \Pr(X = 2)$

2. $\displaystyle \Pr(X \geq 2) = 1 - \Pr(X \leq 1)$

3. $\displaystyle \Pr(X = 0)$.
• Oct 6th 2008, 03:56 AM
Kai
Quote:

Originally Posted by Sameera
Probabaility that a pen manufactured by a company will be defective is 1/10.If 12 such pen are manufacturd,find yhe probability for?

1. exactly two will be defective
2. at least two will be defective
3.none will be defective

THANKS !!!!!!

Hi,

Make use of binomial distribution

X~B(n,p) where n is the number of pens(12 in ur case) and p is the probability of success ( for u case, its to get a defective pen which is 0.1)

Now calculate P(X=2) and so on...

Hope it helps