Difficulty: Medium
Correct Answer: 1584
Explanation:
Introduction / Context:
We distribute distinct items between two labeled recipients with a fixed split of counts. There are two symmetric cases: Rahul gets 5 (Rohan 7) or Rahul gets 7 (Rohan 5).
Given Data / Assumptions (clarified):
Concept / Approach:
Case-split by who gets 5: choose 5 for Rahul (C(12,5)), or choose 5 for Rohan (another C(12,5)). These cases are disjoint and cover all valid allocations.
Step-by-Step Solution:
Number of 5-ball subsets = C(12,5) = 792.Two choices for who receives 5 ⇒ total = 2 * 792 = 1584.
Verification / Alternative check:
Equivalently, choose which 7 go to the 7-ball recipient: 2*C(12,7) = 2*792 = 1584 (since C(12,5)=C(12,7)).
Why Other Options Are Wrong:
Values near 1600 come from arithmetic slips; 1784/1560/1854 are not equal to 2*C(12,5).
Common Pitfalls:
Answering C(12,5)=792 only (implicitly fixing which boy gets 5) despite the statement allowing either boy to be the 5-ball recipient.
Final Answer:
1584
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