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There are 10 professors and 20 lecturers out of whom a committee of 2 professors and 3 lecturer is to be formed. Find:

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प्रश्न

There are 10 professors and 20 lecturers out of whom a committee of 2 professors and 3 lecturer is to be formed. Find:

C1 C2
(a) In how many ways committee: can be formed (i) 10C2 × 19C3 
(b) In how many ways a particular: professor is included (ii) 10C2 × 19C2
(c) In how many ways a particular: lecturer is included (iii) 9C1 × 20C3
(d) In how many ways a particular: lecturer is excluded (iv) 10C2 × 20C3
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उत्तर

C1 C2
(a) In how many ways committee: can be formed (i) 10C2 × 20C3
(b) In how many ways a particular: professor is included (ii) 9C1 × 20C3
(c) In how many ways a particular: lecturer is included (iii) 10C2 × 19C2
(d) In how many ways a particular: lecturer is excluded (iv) 10C2 × 19C3

Explanation:

(a) We have to select 2 professor out of 10 and 3 lecturers out of 20

∴ Number of ways of selection = 10C2 × 20C

(b) When a particular professor is included taken the number of ways = `""^(10 – 1)"C"_1` × 20C3

= 9C1 × 20C3

(c) When a particular lecturer is included then number of ways = 10C2 × 19C2

(d) When a particular lecturer is excluded, then number of ways = 10C2 × 19C3 

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अध्याय 7: Permutations and Combinations - Exercise [पृष्ठ १२८]

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एनसीईआरटी एक्झांप्लर Mathematics Exemplar [English] Class 11
अध्याय 7 Permutations and Combinations
Exercise | Q 62 | पृष्ठ १२८

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