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CLASS_11_MATHS_SOLUTIONS_NCERT

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Class XI Chapter 7 – Permutation and Combination Maths<br />

______________________________________________________________________________<br />

(ii)<br />

2n<br />

n<br />

C<br />

C<br />

<br />

<br />

3<br />

3<br />

<br />

<br />

<strong>11</strong><br />

1<br />

2 n ! 3! n<br />

3 !<br />

<strong>11</strong><br />

3! 2n<br />

3 ! n!<br />

<br />

<br />

<br />

<br />

<br />

<br />

<br />

<br />

2n 2n 1 2n 2 2n 3 ! n 3 !<br />

<br />

2n 3 ! n n 1 n 2 n 3 !<br />

n<br />

n<br />

<br />

n1n2<br />

2 2 1 2 2<br />

<br />

n<br />

n<br />

<br />

n1n2<br />

4 2 1 1<br />

<br />

<br />

4 2n<br />

1<br />

<br />

n 2<br />

<br />

<strong>11</strong><br />

<strong>11</strong><br />

<strong>11</strong><br />

n n<br />

<br />

4 2 1 <strong>11</strong> 2<br />

8n 4 <strong>11</strong>n<br />

22<br />

<strong>11</strong>n 8n 4 22<br />

3n<br />

18<br />

n<br />

6<br />

Question 3:<br />

How many chords can be drawn through 21 points on a circle?<br />

Solution 3:<br />

For drawing one chord a circle, only 2 points are required.<br />

To know the number of chords that can be drawn through the given 21 points on a circle, the<br />

number of combinations have to be counted.<br />

Therefore, there will be as many chords as there are combinations of 21 points taken 2 at a time.<br />

21 21! 21! 2120<br />

Thus, required number of chords C2<br />

210<br />

2! 21<br />

2 ! 2!19! 2<br />

<br />

<br />

Question 4:<br />

In how many ways can a team of 3 boys and 3 girls be selected from 5 boys and 4 girls?<br />

Solution 4:<br />

A team of 3 boys and 3 girls is to be selected from 5 boys and 4 girls.<br />

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