# Thread: binomial formula, probability problem.

1. ## binomial formula, probability problem.

a factory is known to make 15% defectives.
Most of the products are found and fixed or thrown out. Suppose two products are randomly selected for inspection.

1. What is the probability that both pieces are defect free?

2. Suppose at least one of the pieces has a flaw. What is the probablility that both are defective?

I know the binomial theorem can be useful here.
P(x=k) = (n/k)P^k(1-p)^(n-k)

also I did know that if neither piece is defect free:

2/0 .. .85^0*(1-.85)^2
=1*(.15)^2
=.0225

2. ## Re: binomial formula, probability problem.

Originally Posted by rcmango
a factory is known to make 15% defectives.
Most of the products are found and fixed or thrown out. Suppose two products are randomly selected for inspection.

1. What is the probability that both pieces are defect free?

2. Suppose at least one of the pieces has a flaw. What is the probablility that both are defective?

I know the binomial theorem can be useful here.
P(x=k) = (n/k)P^k(1-p)^(n-k)