A video movie store owner finds that 30% of the customers entering the store ask an assistant for help and that 20% of the customers make a purchase before leaving. It is also found that 15% of all...

A video movie store owner finds that 30% of the customers entering the store ask an assistant for help and that 20% of the customers make a purchase before leaving. It is also found that 15% of all customers both ask for assistance and make a purchase. What is the probability that a customer does at least one of these two things?