##### The following problem refers to strings in A, B, ..., Z.

 Mathematics Tutor: None Selected Time limit: 1 Day

Jun 21st, 2015

If repetition  of digits are allowed then

First place can be filled only by S = 1

second place can be filled by  , 26 ways (a ,b,c -----z)  ... similarly third & fourth  : 26 ways each

hence total ways = 1*26*26*26 =17576  (Answer)

If repetition  of digits is not  allowed then

First place can be filled only by S = 1

second place can be filled by  , 25P1 = 25!/24! = 25 ways

third  place can be filled by  , 24P1 = 24!/23! = 24 ways

& fourth place can be filled by  , 23P1 = 23!/22! = 23 ways

hence total string possible = 1*25*24*23 =  13800  (Answer)

please confirm repetation is allowed or not   & According choose the correct answer from above 2

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Jun 21st, 2015

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