19 (Requires use of a spreadsheet) An average of 140 people per year apply for public housing in Boston. An average of 20 housing units per year become available.

During a given year, there is a 10% chance that a family on the waiting list will find private housing and remove themselves from the list. Assume that all relevant random variables are exponentially distributed.

a On the average, how many families will be on the waiting list?

b On the average, how much time will a family spend on the list before obtaining housing (either public or private)?

For the last question, remember that L  lW!