number of ways by which 4digit no made where aless than b,bless than c,c less than d where all lies between 1 to 9

• we have to make 4 digit number
  in which the format is d> c > b > a
  __ __ __ __
  
  1st position can be filled by 6 digits(9, 8, 7, 6, 5, 4)
  2nd position can be filled by 6 digits(8, 7, 6, 5, 4, 3)
  3rd position can be filled by 6 digits(7, 6, 5, 4, 3, 2)
  4th position can be filled by 6 digits(6, 5, 4, 3, 2, 1)
  
  hence every place can be filled by 6 digits,
  6* 6* 6* 6 = 1296
  
  
  
• 7 years agoHelpfull: Yes(6) No(4)
• the correct answer is 126
  there are 9 digits to select from 1,2,3,4,5,6,7,8,9
  now we have to form 4 digit number .So the total number of selection of 4 digit number is C(9,4).
  Now within any selection there is only one possible way to arrange the digits otherwise condition is not satisfied if the digits are arranged.
  So the answer is given as C(9,4)*1 =126
• 7 years agoHelpfull: Yes(4) No(4)
• b c d a
  9 8 7 6-1way
  8 7 6 5-+1
  7 6 5 4-+1
  6 5 4 3 -+1
  5 4 3 2 -+1
  4 3 2 1 -+1
  ------
  6 ways
• 7 years agoHelpfull: Yes(1) No(9)
• means a
• 7 years agoHelpfull: Yes(0) No(1)