Question

The Write Right Company manufactures ballpoint pens and has been experiencing a 5% rate of defective pens. Suppose a random sample of 11 pens is taken.

What is the probability that exactly 1 pens are defective ?

Answer 1

@dyoung8907

This is binomial probability.

The probability of a defective pen is .05.
Therefore, the probability of a defective pen is .95.

Of the 11 pens, one is defective (in this problem).
But, you don't know if it is the first, second, third, or on down the line to the 11th selected pen that is faulty.

P(exactly 1 defect) = 11* (.05)^1 times (.95) ^ 10
Crank that out to get the probability.