Question 1194442
1. How many different 4-digit numbers can be formed from the digits 2, 3, 4, 5, 6, 7, and 9: 
a) if repetition of digits is NOT allowed?
There are 7 numbers.
The 1st choice is 1 of 7, then 1 of 6, 1 of 5, 1 of 4.
---> 7*6*5*4
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 b) if repetition of digits is allowed? 
Each selection is 1 of 7 ---> 7*7*7*7
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c) How many of them are odd numbers?
With or without repetition?
 d) How many of them are even numbers?
With or without repetition?