in P& C if no condition is mentioned then always assume that repetation is not allowed.

see,[ no. of pemutation of n dissimilar things taken r at a time]

nPr = n!/(n-r)!

= n(n-1)(n-2)....(n-r+1)

hence last factor is [n -(r-1)] = n-r+1

where , n!= 1*.2*.3........n

note: n! = n(n-1)*(n-2)! etc.

this is the general form.

but if repetation is allowed then ,

in this  case , each of the r places can be filled in n ways.

hence by fundamental theorm, all r places can be filled in n* n* n*n.... r times = n^r.

hence we see that this has been derived from the fundamental theorm.

so, if no condition is mentioned then we always consider that repetation is not allowed.

 

did u get my logic.???

 

 if so then ,

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