(Original?) Brain teaser

There are 2 apartments, A and B. Apartment A has 10 tenants and 2 washing machines; apartment B has 20 tenants and 4 washing machines. If your objective is to minimize the probability that all machines are occupied when you want to do laundry, which one is better, A or B, or does it not matter? Assume that ‘Tenant i does laundry at time t’ follows mutually independent Poisson processes. Assume also that each and every laundry takes the same finite amount of time T.