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January 25, 2015

January 25, 2015

Posted by **Vicky** on Thursday, September 11, 2008 at 4:01pm.

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**David Q**, Thursday, September 11, 2008 at 4:05pmIt's a question about factorials: the answer is the number of ways you can choose 3 from 5. You could enumerate them without too much difficulty, but the shortcut is to work out 5! / (3! x (5-3)!), where N! means N x (N-1) x (N-2) .... x 2 x 1.

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**Reiny**, Thursday, September 11, 2008 at 4:07pmthink of it this way:

The pizzamaker would have 5 ways to choose the first topping, then 4 ways to do the second topping and finally 3 ways for the third topping

so isn't that 5x4x3 or 60 ways

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**David Q**, Thursday, September 11, 2008 at 4:09pmNo - you're distinguishing between the 1st, 2nd and 3rd, which you don't need to do. ABC is the same as BCA, which is the same as CAB etc. You've got to allow for all the combinations that are the same.

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**Reiny**, Thursday, September 11, 2008 at 4:10pmDavid is correct, I was in error

My senior moment of the day.

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**David Q**, Thursday, September 11, 2008 at 4:10pmIn fact, every triple can occur in six different ways - so the answer is actually the 60 you identified, divided by 6.

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**Vicky**, Thursday, September 11, 2008 at 4:19pmI'm in 6th grade and never heard of using ! in math. I guess I'll do it the long way to see how it works. Thanks so much :)

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**Kristin;**, Thursday, September 11, 2008 at 7:41pmdo 5x3..

its fifteen(:

these ppl are so confusingg;

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**David Q.**, Sunday, September 14, 2008 at 1:39pmJust for the record the answer is ten. They are: ABC, ABD, ABE, ACD, ACE, ADE, BCD, BCE, BDE and CDE.

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