Help with counting problem
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Help with counting problem

[From: ] [author: ] [Date: 12-02-29] [Hit: ]
Can you answer and explain? Thanks-3 choices for letter,......
Sue wants to create several different 7-character screen names. She wants to use arrangements of the letters of her first name (sue), followed by arrangements of four digits in 1984, the year of her birth. How many different screen names can she create if, a) repeating allowed, and b) repeating not allowed?

I don't understand this at all. Can you answer and explain? Thanks

-
3 choices for letter, 4 choices for numbers
can repeat = 3*3*3*4*4*4*4 = 6912

no repeat = 3*2*1*4*3*2*1 = 144
1
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