Three boys of class X, four boys of class XI, and five boys of class XII sit in a row. The total number of ways in which these boys can sit so that all the boys of same class sit together is equal to

We can think of three packets. one consisting of three boys of class X, other consisting of 4 boys of class XI and last one consisting of 5 boys of class XII. These packets can be arranged in it ways and contents of these packets can be number arranged in 31 4! and 5 ! ways, respectively. Hence, the total number of ways is 3 !x 3 ! x 4! x 5 !