>>in how many ways we can select 3 persons sitting in row from 10 persons such thatadjacent persons are not selected?>>

In order to select 3 persons froma group of 10, this can be done in: 10C3 ways = 120 ways

now the restriction is that 2 or 3 adjacent persons hsld not be selected

let the persons be : - - - - - - - - - -

here there are 8 sets of adjacent persons and the third person can be taken  from any of 8( which includes 3 adjacent persons too)

this can be done in = 8x9 =72 ways

the answer is : 120 - 72 = 48 ways

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Regards

Ramesh