13.A manufacturer produced 100 computers and shipped them to a distributer. Twenty of the computers were defective. The distributor will accept the shipment if four randomly chosen computers (without replacement) are good. What is the probability at least one is defective?

14. How many different license plates can be made in a state if the plate has three letters followed by 4 numbers?

15. How many ways can you select 4 students in a class of 20 students to work on a project together?

16. A student club has 12 members. In how many ways can they choose 4 different students to serve as president, vice president, secretary, and treasurer?