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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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