# The probability that one 3 foot section of wire is defective is 0.002.

1. Oct 23, 2011

### glebovg

The probability that one 3 foot section of wire is defective is 0.002. If someone has 450 feet of wire then what is the probability they will have 3 or more 3 feet sections that are defective?

2. Oct 23, 2011

### LCKurtz

Re: Probability

What have you tried?

3. Oct 23, 2011

### cmb

Re: Probability

I'm getting the feeling that there isn't enough information here. I think the term "probability that one 3 foot section of wire is defective is 0.002" could be interpreted in a number of ways.

4. Oct 23, 2011

### LCKurtz

Re: Probability

I agree it is pretty ambiguous. But one could assume we are talking about dividing the wire into 150 separate 3 foot sections and interpret it that way just to have something to talk about.

5. Oct 23, 2011

### glebovg

Re: Probability

That is exactly what I think. At first I thought that X~Pois(λ) and that P(X=1)=0.002. But finding λ seems impossible and even the values you find do not make any sense.

6. Oct 23, 2011

### glebovg

Re: Probability

Perhaps X~Bin(150, 0.002).

7. Oct 23, 2011

### LCKurtz

Re: Probability

That's what I would try (making an independence assumption).

8. Oct 24, 2011

### Ray Vickson

Re: Probability

Well, you have a large N, small p version of the binomial, with m = N*p "moderate", so I think a Poisson approximation should be very good, indeed.

RGV

9. Oct 25, 2011

### glebovg

Re: Probability

Thank you.