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NCERT · Class 11 · Maths

Chapter 7: Permutations and Combinations Exercise 7.2

Practice each question, then open the answer or worked solution.

Questions

5 questions
Q1Written answer

Evaluate
(i) 8!

(ii) 4! – 3!

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Worked solution

(i) Consider 8!

We know that 8! = 8 × 7 × 6 × 5 × 4 × 3 × 2 × 1

= 40320

(ii) Consider 4!-3!

4!-3! = (4 × 3!) – 3!

Above equation can be written as

= 3! (4-1)

= 3 × 2 × 1 × 3

= 18

Q2Written answer

Is 3! + 4! = 7!?

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Worked solution

Consider LHS 3! + 4!

Computing left hand side, we get

3! + 4! = (3 × 2 × 1) + (4 × 3 × 2 × 1)

= 6 + 24

= 30

Again considering RHS and computing, we get

7! = 7 × 6 × 5 × 4 × 3 × 2 × 1 = 5040

Therefore LHS ≠ RHS

Therefore 3! + 4! ≠ 7!

Q3Written answer

Compute 

NCERT Solutions for Class 11 Maths Chapter 7 Permutations and Combinations Image 1

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Worked solution

 NCERT Solutions for Class 11 Maths Chapter 7 Permutations and Combinations Image 2

Q4Written answer

If NCERT Solutions for Class 11 Maths Chapter 7 Permutations and Combinations Image 3find x.

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Worked solution

NCERT Solutions for Class 11 Maths Chapter 7 Permutations and Combinations Image 4

Q5Written answer

Evaluate

 NCERT Solutions for Class 11 Maths Chapter 7 Permutations and Combinations Image 5,

When
(i) n = 6, r = 2
(ii) n = 9, r = 5

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Worked solution

NCERT Solutions for Class 11 Maths Chapter 7 Permutations and Combinations Image 6

Access Other Exercise Solutions of Class 11 Maths Chapter 7 – Permutations and Combinations

Exercise 7.1 Solutions 6 Questions

Exercise 7.3 Solutions 11 Questions

Exercise 7.4 Solutions 9 Questions

Miscellaneous Exercise On Chapter 7 Solutions 11 Questions

Also explore – NCERT Class 11 Solutions