CMA Foundation · Fundamentals of Business Mathematics and Statistics · Permutation and Combinations
Five friends, Arun, Bala, Charu, Deepa and Esha, sit in a row for a photograph. If Arun and Bala must always sit next to each other, in how many ways can they be arranged?
The answer is 48. Treating Arun and Bala as a single block gives 4 units, arranged in 4! = 24 ways, and the two can swap places within the block in 2 ways, so 24 × 2 = 48 arrangements.
- A24
- B48Correct
- C60
- D120
Explanation
Treat Arun and Bala as one block: 4 units can be arranged in 4! = 24 ways. The pair can be ordered internally in 2! = 2 ways, giving 24 × 2 = 48. The value 24 forgets the internal order of the pair.
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One question tells you little. A timed set on Permutation and Combinations shows your real accuracy, how long you take and where you lose marks.
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