# Binomial Distributions Question

• Apr 17th 2010, 02:57 PM
asemh
Binomial Distributions Question
Hi
Im having trouble doing this question.
Could someone help me out.

A factory produces computer chips with a 0.9% defect rate. In a batch of 100 computer chips, what is the probability that

a) only 1 is defective?
b) at least 3 are defective?

I guessed that p = 0.9 and q = 0.1 and n = 100

For a) I tried (100 Choose 1)*(0.9)^1 * (0.1)^99
but it turned out wrong..

The answers in the back of the book were a) 36.8% and b) 6.2%

How did they get these values?

• Apr 17th 2010, 04:13 PM
Soroban
Hello, asemh!

Quote:

A factory produces computer chips with a 0.9% defect rate.
In a batch of 100 computer chips, what is the probability that

a) only 1 is defective?

b) at least 3 are defective?

I guessed that p = 0.9 and q = 0.1 . $\displaystyle {\color{blue}\leftarrow\;\text{Here!}}$

Careful . . . $\displaystyle p \:=\:0.9\% \:=\:0.009$

• Apr 17th 2010, 04:20 PM
pickslides
Quote:

Originally Posted by asemh

A factory produces computer chips with a 0.9% defect rate. In a

You are not considering the % sign

0.9% $\displaystyle \implies p = 0.009$ . This will give you the answer you require.
• Apr 17th 2010, 05:18 PM
asemh
oooh!!
Thanks a lot
I thought they already converted it into decimals
Thanks