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 $4.00. What is the percentage of items that cost:
a. Less than $2.00? (Round your answer to 4 decimal places.)
b. More than $3.00? (Round your answer to 4 decimal places.)
c. Between $2.50 and $3.50? (Round your answer to 4 decimal places.)
d. Find the 20th percentile. Eighty percent of the supermarket items cost more than what amount?(Round your answer to 2 decimal places.)