NCERT Solutions for Class 11 Maths Chapter 7 Permutations and Combinations Ex 7.2 are part of NCERT Solutions for Class 11 Maths. Here we have given NCERT Solutions for Class 11 Maths Chapter 7 Permutations and Combinations Ex 7.2.

- Permutations and Combinations Class 11 Ex 7.1
- Permutations and Combinations Class 11 Ex 7.3
- Permutations and Combinations Class 11 Ex 7.4

Board |
CBSE |

Textbook |
NCERT |

Class |
Class 11 |

Subject |
Maths |

Chapter |
Chapter 7 |

Chapter Name |
Permutations and Combinations |

Exercise |
Ex 7.2 |

Number of Questions Solved |
5 |

Category |
NCERT Solutions |

## NCERT Solutions for Class 11 Maths Chapter 7 Permutations and Combinations Ex 7.2

**Ex 7.2 Class 11 Maths Question 1.**

Evaluate

(i) 8!

(ii) 4!-3!

**Solution.**

**(i)** 8! = 1 x 2 x 3 x 4 x 5 x 6 x 7 x 8 = 40320

**(ii)** 4! – 3! = (1 x 2 x 3 x 4) – (1 x 2 x 3) = 24 – 6 = 18

**Ex 7.2 Class 11 Maths Question 2.**

Is 3! + 4! = 7! ?

**Solution.**

3! + 4! = (1 x 2 x 3) + (1 x 2 x 3 x 4) = 6 + 24 = 30 … (i)

7! = 1 x 2 x 3 x 4 x 5 x 6 x 7 = 5040 ………(ii)

From (i) & (ii), we get 3! + 4! ≠ 7!.

**Ex 7.2 Class 11 Maths Question 3.**

\(\frac { 8! }{ 6!\times 2! } \)

**Solution.**

\(\frac { 8! }{ 6!\times 2! } =\frac { 8\times 7\times 6! }{ 6!\times 2! } =4\times 7=28\)

**Ex 7.2 Class 11 Maths Question 4.**

\(\frac { 1 }{ 6! } +\frac { 1 }{ 7! } =\frac { x }{ 8! } \), findx.

**Solution.**

We have, \(\frac { 1 }{ 6! } +\frac { 1 }{ 7! } =\frac { x }{ 8! } \)

**Ex 7.2 Class 11 Maths Question 5.**

Evaluate \(\frac { n! }{ \left( n-r \right) ! } \), when

(i) n = 6, r = 2

(ii) n = 9, r = 5

**Solution.**

**(i)** \(\frac { 6! }{ \left( 6-2 \right) ! } =\frac { 6! }{ 4! } =\frac { 6\times 5\times 4! }{ 4! } =30\)

**(ii)** \(\frac { 9! }{ \left( 9-5 \right) ! } =\frac { 9! }{ 4! } =\frac { 9\times 8\times 7\times 6\times 5\times 4! }{ 4! } =15120\)

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