The cost per item at a supermarket follows an exponential distribution. There are many inexpensive items and

Question:

The cost per item at a supermarket follows an exponential distribution. There are many inexpensive items and a few relatively expensive ones. The mean cost per item is $3.50. What is the percentage of items that cost:
a. Less than $1?
b. More than $4?
c. Between $2 and $3?
d. Find the 40th percentile. Sixty percent of the supermarket items cost more than what amount?