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Sarah wants to order a pizza with 2 different toppings. She has 9 different toppings to choose from. How many different pizzas could she order?

 Feb 28, 2021
 #1
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In her first topping, she has 9 choices. 

In her second topping, she has 8 choices. (not 9 because it can't be the first one she chose)

9*8 = 72 options. 

However, we have to consider that choosing a then b is the same as choosing b then a.

For example, choosing peppers then sausage is the same as sausage then peppers, so we have to divide by 2.

72/2 = 36. 

36 options. :))

 

=^._.^=

 Feb 28, 2021
 #2
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9 c 2 = 36      9! / (7! 2!) = 36

 Feb 28, 2021
 #3
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Thank you both!

 Feb 28, 2021

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