In how many ways can four children be made to stand in a line such that two of them, A and B are always together ?
In how many ways can four children be made to stand in a line such that two of them, A and B are always together ?
Answer:
(b)
To solve the problem, we can consider A and B as a single unit. This gives us three units to arrange – AB, C, and D. Now, we can arrange these three units in 3! ways = 6 ways. Within the AB unit, there are two ways to arrange A and B. Therefore, the total number of ways to arrange the four children such that A and B are always together is 6 x 2 = 12.