Multiple choice

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?

  1. 6

  2. 12

  3. 18

  4. 24

  5. NOTA
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Treat A and B as a single unit. There are 3 units (AB, C, D) to arrange in 3! = 6 ways. Within the unit, A and B can be arranged in 2! = 2 ways. Total = 6 * 2 = 12.

AI explanation

To solve this, treat the two specific children, A and B, as a single combined unit, which means you are now arranging 3 units in a line. These 3 units can be arranged in 3 factorial ways, and the children A and B can switch places within their unit in 2 factorial ways. Multiplying these together gives 3 factorial x 2 factorial = 6 x 2 = 12 ways.

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