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Jack
10-10-2013, 11:27 AM
How many different 4-digit numbers can be formed using all of the following numbers?
0,1,1,9
(A) 4
(B) 12
(C) 16
(D) 24

thanks

miranda
10-10-2013, 11:31 AM
In this case we have permutations since the order matters. Additionally we must divide the number of permutations by 2! Since the digit “1” appears twice.
Therefore the answer is \frac{^4P_{4}}{2!}=\frac{4!}{2!}=12 (B).

Jack
10-10-2013, 11:32 AM
thank you!!