If 5 students are seated at random in a row,the probability that two particular students are not seated side by side is
a)13/120 b)119/120 c)3/5 d)4/5

• Ans is (c) 3/5
  Total ways of sitting= !5=120
  Ways in which 2 students sit together= !4*!2=48 (take 2 students as 1 single unit so 5-1=4 and also these 2 students can arrange themselves in !2 ways)
  Therefore,P(2 students sit together) =48/120
  And so P(2 students dont sit together)=1-48/12₩=72/120=18/30=6/10=3/5
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