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

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.

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! }
NCERT Solutions for Class 11 Maths Chapter 7 Permutations and Combinations Ex 7.2 1

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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