Question

5 boys of class VI, 6 boys of class VII and 7 boys of class VIII sit in a row. The number of ways they can sit so that boys of the same class sit together, is

(a) (5!)(6!)(7!)

(b) (3!)(5!)(6!) (7!)

(c) 18!/(5!6!7!)

(d) (4!)(5!)(6!)

Answer 1

Correct option (b) (3!)(5!)(6!) (7!)

Explanation:

Boys of class VI can sit among each other in 5! ways Boys of class VII can sit among each other in 6! ways Boys of class VIII can sit among each other in 7! ways As boys of each class sit together, so we have 3 groups which can be organised in 3! ways.

Hence the number of ways = 3! 5! 6! 7!