Biology and Math Help Please!?

Question

In humans, the rate of mutation is about 1 in 100,000. You have about 100,000 genes. What is the chance that you have a gene that has a mutation and is, different from any of the genes our mother and father have?

Answer 1

The answer is approximately (1 - 1/e). To find it exactly, you have to find the probability of not having a mutation and substract from one. The probablity of not having a mutation is given 100,000 genes is

( 1 - 1/100,000) ^ 100,000

That is a pretty good approximation for 1/e, hence my first answer.