How many ways can you arrange the letters in the word 'CAT'?

If you have 4 friends, and you can only invite 2 to a party, how many different groups of friends could you invite?

A restaurant offers 3 appetizers, 5 main courses, and 2 desserts. How many different 3-course meals are possible?

How many different ways can you order a pizza with 3 toppings if there are 6 toppings to choose from, and you can't repeat a topping?

In how many ways can a team of 11 players be selected from 15 players?