How many permutations of the letters ABCDEFGH

A. Contain ED

  • I thought of ED as one letter and the rest as separate.

then there is only one way to make ED = 1! and 7! ways to rearrange them together= 7!

Answer: 7!1!= 5040

I think the same concept can be used for the rest.

E .

  • you can count CABED as one word

4!

F. Not possible 0

This is a great way to think about it, and it's how I did it. --Norlow 22:14, 17 September 2008 (UTC)

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Ph.D. on Applied Mathematics in Aug 2007. Involved on applications of image super-resolution to electron microscopy

Francisco Blanco-Silva