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

[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?

 

[LCKurtz]

What have you tried?

 

[cmb]

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.

 

[LCKurtz]

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.

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.

 

[glebovg]

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.

 

[glebovg]

Perhaps X~Bin(150, 0.002).

 

[LCKurtz]

Perhaps X~Bin(150, 0.002).

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

 

[Ray Vickson]

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.

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

 

[glebovg]

Thank you.