Ten different letters of alphabets are given , words with 5 letters are formed from these given letters . then , the number of words which have at least one letter repeated is : ans - 69760

• no of words when repetition allowed is 10*10*10*10*10=100000
  no of words when non repeated is 10p4=30240
  no of words atleast 1 letter repeated is 100000-30240=69760
  
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• 1st possible total no of words repeated
  10p1*10p1*10p1*10p1*10p1=10*10*10*10*10=100000
  
  2nd possible total no of words that is not repeated
  10p1*9p1*8p1*7p1*6p1=10*9*8*7*6=30240
  
  therefore 10000-30240=69760 is the possible of getting atleast one letter is repeated
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