SOLUTION: How many four-digit numbers can be formed using the digits 1,2,3,4,5,6,7,8, and 9. a) if repetition is allowed? b) if repetition is not allowed? c) How many of 4 digits numbers

Algebra ->  Permutations -> SOLUTION: How many four-digit numbers can be formed using the digits 1,2,3,4,5,6,7,8, and 9. a) if repetition is allowed? b) if repetition is not allowed? c) How many of 4 digits numbers       Log On


   

Question 1072909: How many four-digit numbers can be formed using the digits 1,2,3,4,5,6,7,8, and 9.
a) if repetition is allowed?
b) if repetition is not allowed?
c) How many of 4 digits numbers in (a) are greater than 6000?
Answer by Fombitz(32388) About Me  (Show Source):
You can put this solution on YOUR website!
a)N=9%2A9%2A9%2A9=6561
b) N=9%2A8%2A7%2A6=3024
c) Look at numbers starting in 6,
N=9%2A9%2A9
Same number for numbers starting in 7,8, and 9.
So there are 4 sets of 9*9*9.
N%5Btot%5D=4%2A9%2A9%2A9
N%5Btot%5D=2916