How many 10-digit numbers have at least 2 equal digits?

• Number of 10 digit numbers with no digit equal= 9*9!
  Total 10 digit numbers are= 9*10^9
  So, number of 10 digit no.s with at least 2 equal digit is->
  (9*10^9)-(9*9!) (Ans).
• 8 years agoHelpfull: Yes(29) No(2)
• we have 10 digit and at least 2 digits are equal...
  
  lets 1st digit as 1 so 1 _ _ _ _ _ _ _ _ _ so wthin 9 places atleast 1 place must be 1 so remaining 8 places we can fill it up with any digit(0-9)
  which results you 10^8 possibilities.
  
  Now lets 1st digit as 2 so 2 _ _ _ _ _ _ _ _ _ so within 9 places at least 1 place must be 2 so remaining 8 places we can fill it up with any digit(0-9)
  which results you 10^8 possibilities.
  
  so we will get 10^8+10^8+10^8+10^8+10^8+10^8+10^8+10^8+10^8 = 9*10^8
• 8 years agoHelpfull: Yes(0) No(3)
• becoz........................there are two bags so we have check the probability among those bags =1/2..........
  
  total bags=2,chance is 1 so 1/2.
• 8 years agoHelpfull: Yes(0) No(2)