The time (in minutes) between telephone calls at an insurance claims office has the exponential probability distribution:

The time (in minutes) between telephone calls at an insurance claims office has the exponential probability distribution
f(x) = 0.50 e-0.50x for x ≥ 0.
what is probability of 30 seconds or less between phone calls.
If this is the complete question.
First, convert 30 seconds to .5 minutes. The mean time between phonecall is u=2.
P(x is less than .5)1-e^5/2= 0.2212
So the answer was approximately 22%.