Answer: d. .2474.
Step-by-step explanation:
Given : The cashier service time at the local branch of the Rivertown bank has an exponential distribution with a mean of 2.5 minutes.
The cumulative distribution function for exponential distribution is :-
, where = Mean of the distribution.
The probability that the service time is between 2 and 4 minutes will be :
Hence, the correct option is d. .2474.