# Math Help - Exponential probability

1. ## Exponential probability

A Department of repairing machines receives an average of five calls per hour. Starting at a randomly chosen point of time, the probability that the first call comes in half an hour is?

The answer is: 0,91792

But, I find:

$e^{-\frac{1}{5}0,5} = 0,9048$

2. Are you sure that the underlying distribution is an exponential?

3. Originally Posted by matheagle
Are you sure that the underlying distribution is an exponential?
Yes