Multiple choice

In how many different ways can books A, B, C, D be piled up such that A comes exactly in between C and D?

  1. 4

  2. 2

  3. 1

  4. 3

  5. 24
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A Correct answer
AI explanation

Books C and D must be on either side of A, meaning the block can be CAD or DAC, giving 2 arrangements for the group. This block of three books combines with book B to form two items to pile up, which can be arranged in 2 factorial ways. The total number of ways is 2 arrangements for the block times 2 positions for the block, resulting in 4.

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