3. The Springdale High School band is performing a benefit jazz concert in its new 4OO-seat auditorium. Local businesses buy the tickets in blocks of 10 and donate them to youth organizations.

Tickets go on sale to business entities for 4 hours only the day before the concert. The process of placing orders for tickets is Poisson with a mean 10 calls per hour.

Any (blocks of) tickets remaining after the box office is closed are sold at a discount as

"rush tickets" 1 hour before the concert starts. Determine

(a) The probability that it will be possible to buy rush tickets.

(b) The average number of rush tickets available.