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Permutations and Combinations
Permutations, Grouping
jee_main_2026_april_4_shift_2
Grade 12
Question:
In how many ways can 4 distinct books be arranged on a shelf such that two specific books are always together and the other two are also always together?
A. 4
B. 6
C. 8
D. 12
Step-by-Step Solution
Key Concept: Treat each pair as a single unit, then arrange the two units.
Step 1: Treat the two specific books as one unit (Pair 1) and the other two as another unit (Pair 2). Step 2: Total units = 2. Arrangements of 2 units = 2! = 2. Step 3: Internal arrangements: Pair 1 has 2! = 2 ways, Pair 2 has 2! = 2 ways. Step 4: Total arrangements = 2 × 2 × 2 = 8.
Correct Answer:C
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