Math Help Forum - View Single Post - What is the difference between Selections and Arrangements/Permutaions?

22upon7 · #3 November 5th, 2009, 11:49 PM

Quote:

Originally Posted by Robb

So, three letters are chosen randomly and arranged in a row. There are $5P3=60$ ways they can be arranged... Since you want the first letter to be a H, there is only one way that can happen, and there is $4P2=12$ ways that can happen. So $Pr(\mbox{H is first})=\frac{1\cdot 12}{60}=\frac{1}{5}$

Thanks Robb, I didn't understand this bit though, could you help me out with it?:

Quote:

Originally Posted by Robb

Since you want the first letter to be a H, there is only one way that can happen, and there is $4P2=12$ ways that can happen.

Thanks again,

Dru