(a) There are ten places, where the boys can be seated. Now, a2 cannot come at 9th and 10th positions otherwise condition is not fulfilled. ∴ Total number of ways the boys can be arranged in 8 places regarding a2 = 8! Similarly for a5, he cannot be seated in first place and at the 10th place, then possible ways of arrangement = 8! Now, a7 cannot be seated on 1st and 2nd places, then possible number of ways = 8! ∴ Total number of w s = 8! + 8! + 8! = 3 x 8 !