**NCERT Solutions for Class 11 Maths Chapter 7 Permutations and
Combinations Ex 7.4**

NCERT Solutions for Class
11 Maths Chapter 7
Permutations and Combinations Ex 7.4 are the part of NCERT Solutions for Class
11 Maths. Here you can find the NCERT Solutions for Class 11 Maths chapter 7
Permutations and Combinations Ex 7.4.

**Ex 7.4 Class 11 Maths Question 1.**

lf ^{n}C

_{8}=

^{n}C

_{2}, find

^{n}C

_{2}.

**Solution.**

Given, ^{n}C_{8} = ^{n}C_{2}

**Ex 7.4 Class 11
Maths Question 2.**

Determine n if**(i)**

^{2n}C

_{3 }:

^{n}C

_{3}= 12 : 1

**(ii)**

^{2n}C

_{3 }:

^{n}C

_{3 }= 11 : 1

**Solution.**

**Ex 7.4 Class 11 Maths Question 3.**

How many chords can be drawn through 21 points on a circle?

**Solution.**

A chord is formed by joining two points on a circle.

∴ Required number of chords = ^{21}C_{2}

= 21! / 2! 19! = (21 × 20)/2 = 210

**Ex 7.4 Class 11 Maths Question 4.**

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

**Solution.**

3 boys can be selected from 5 boys in ^{5}C_{3} ways and
3 girls can be selected from 4 girls in ^{4}C_{3} ways.

∴ Required number of ways of team
selection = ^{5}C_{3} × ^{4}C_{3} = 5! / 2! 3! × 4! / 3! 1!

= 5 × 2 × 4 = 40

**Ex 7.4 Class 11
Maths Question 5.**

Find the number of ways of selecting 9 balls from 6 red balls, 5 white balls
and 5 blue balls if each selection consists of 3 balls of each colour.

**Solution.**

The number of ways of selecting 3 red balls = ^{6}C_{3}

The number of ways of selecting 3 white balls = ^{5}C_{3}

The number of ways of selecting 3 blue balls = ^{5}C_{3 }

∴ Required number of ways of selecting 9
balls

**Ex 7.4 Class 11
Maths Question 6.**

Determine the number of 5 cards combinations out of a deck of 52 cards if there
is exactly one ace in each combination.

**Solution.**

Total number of cards = 52

Number of ace cards = 4

Number of non-ace cards = 48

∴ One ace card out of 4 can be selected
in ^{4}C_{1} ways.

Remaining 4 cards out of 48 cards can be selected in ^{48}C_{4 }ways.

∴ Required number of ways of selecting 5
cards

**Ex 7.4 Class 11
Maths Question 7.**

In how many ways can one select a cricket team of eleven from 17 players in
which only 5 players can bowl if each cricket team of 11 must include exactly 4
bowlers?

**Solution.**

Total number of players = 17

Number of bowlers = 5

Number of non-bowlers = 12

Number of ways of selecting 4 bowlers = ^{5}C_{4}

Number of ways of selecting 7 non-bowlers = ^{12}C_{7}

∴ Required number of ways of selecting a
cricket team

**Ex 7.4 Class 11 Maths Question 8.**

A bag contains 5 black and 6 red balls. Determine the number of ways in which 2
black and 3 red balls can be selected.

**Solution.**

Number of ways of selecting 2 black balls = ^{5}C_{2}

Number of ways of selecting 3 red balls = ^{6}C_{3}

∴ Required number of ways of selecting 2
black and 3 red balls = ^{5}C_{2} × ^{6}C_{3}

= 5! / 2! 3! × 6! / 3! 3! = 5 × 2 × 5 × 4 = 200

**Ex 7.4 Class 11 Maths Question 9.**

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 number of courses = 9

Number of compulsory courses = 2

So, the student will choose 3 courses out of 7 courses [non-compulsory
courses].

∴ Required number of ways a student can
choose a programme = ^{7}C_{3} = 7! / 3! 4! = (7 × 6 × 5)/6 = 35

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