Originally Posted by

**tommyf** If I buy 17 new railway sleepers, the specification sheet of which accurately states that 5% sleepers are not cuboid, what is the probability that I find 9 out of 17 of the sleepers on delivery are not cuboid (assuming there are no other confounding influences on shape and that the sleepers are randomly selected)?

This is a real situation - the company supplying the sleepers tells me I've just been unlucky. I want to illustrate my response with the probability of this event happening randomly, which I'm guessing is pretty slim.

Thank you, TommyF (a medic, not a mathematician)