Apizza parlor offers 4 different pizza toppings. how many different kinds of 2-topping pizzas are available?

6 kinds

20 kinds

10 kinds

5 kinds

Order does not matter so use "n choose k" formula is used to find number of unique combinations.

c=n!/(k!(n-k)!)  where n is total possible choices and k is number of selections.

c=4!/(2!(4-2)!)

c=4!/(2!2!)

c=24/(2*2)

c=24/4

c=6

So there are 6 different two topping options when there are four different toppings to choose from.