How many four digit numbers can be formed using digits 1,1,2,2,3,3,4,4

1.	How many four digit numbers can be formed using digits 1,1,2,2,3,3,4,4,5,5
Answer» no. of 4 digit numbers in this case can be fined as 10 ! / 2! . 2! .2! .2! . 2!

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