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A student has to answer 10 questions, choosing atleast 4 from each of Parts A and B. If there are 6 questions in Part A and 7 in Part B, in how many ways can the student choose 10 questions?

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Question

A student has to answer 10 questions, choosing atleast 4 from each of Parts A and B. If there are 6 questions in Part A and 7 in Part B, in how many ways can the student choose 10 questions?

Sum
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Solution

The possibilities are: 4 from Part A and 6 from Part B

or 5 from Part A and 5 from Part B

or 6 from Part A and 4 from Part B.

Therefore, the required number of ways is

6C4 × 7C6 + 6C5 × 7C5 + 6C6 × 7C4

= 105 + 126 + 35

= 266.

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Chapter 7: Permutations and Combinations - Solved Examples [Page 117]

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NCERT Exemplar Mathematics Exemplar [English] Class 11
Chapter 7 Permutations and Combinations
Solved Examples | Q 7 | Page 117

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