How many 7 digit numbers are there having the digit 3 three times and the digit 0 four times.
Ans :15

• _ _ _ _ _ _ _
  7 digits
  First one should be three since.. 0 cannot occupy first digit.
  3 _ _ _ _ _ _
  Now.. the no. Of ways of filling these is 6!
  Also.. we have 2 times 3..and 4 times 0
  6! / ( 2! 4!)
  15
  
  Note : later i said we have only 2 threes.. because one three is fixed at the first position.
• 8 years agoHelpfull: Yes(1) No(0)