The Centurion apartment building in downtown Chicago has a total of 240 rental units. It offers its new tenants an 18-month lease, which is renewed on a month-to-month basis if the tenant chooses to stay longer than 18 months. The leasing office reports that The Centurion signs about 80 leases with new tenants in an average year, and that 60% of tenants who move in end up staying in the building longer than 18 months. On average, the building is 90% occupied.
You may assume that a negligible number of tenants break their lease in the first 18 months.
What is the average number of tenants who are in their first 18 months at The Centurion?
What is the average length of stay (in months) for those tenants who stay longer than 18 months (counted from when they first sign their original lease)?