Problem: Each hour, the ticket seller at the local mall can serve an average of 12 customers every hour, and an average of 10 customers every hour arrive to buy tickets for the Grateful Dead concert. Determine the portion of time the teller is busy.
A) about 50 minutes out of every hour
B) about 30 minutes out of every hour
C) about 25 minutes out of every hour
D) cannot be determined from the information given