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NCERT Class XI Mathematics - Permutations and Combinations - Solutions

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Question : 30 of 41
Marks: +1, -0
In how many ways can a student choose a programme of 5 courses if 9 courses are available and 2 specific courses are compulsory for every student?
Solution:  
Total no. of courses = 9
No. of compulsory courses = 2
So, the student will choose 3 courses out of 7 courses [non compulsory courses].
∴ Required no. of ways a student can choose a programme
=  7C3\,{}^{7}C_3 = 7!3!4!\frac{7!}{3!4!} = 7×6×56\frac{7\times6\times5}{6} = 35
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