Lily estimates that her time to fall asleep each night is approximately Exponential, with an average time of 30 minutes until she falls asleep.
a. What is the probability that it takes her less than 10 minutes to fall asleep?
b. What is the probability that it takes her more than 1 hour to fall asleep?
c. If she has already laid awake for 1 hour, what is the probability that it will take her more than 90 minutes (altogether) to fall asleep?