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

#### Page No 140:

#### Question 1:

Evaluate

(i) 8! (ii) 4! – 3!

#### Answer:

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

(ii) 4! = 1 × 2 × 3 × 4 = 24

3! = 1 × 2 × 3 = 6

∴4! – 3! = 24 – 6 = 18

#### Page No 141:

#### Question 2:

Is 3! + 4! = 7!?

#### Answer:

3! = 1 × 2 × 3 = 6

4! = 1 × 2 × 3 × 4 = 24

∴3! + 4! = 6 + 24 = 30

7! = 1 × 2 × 3 × 4 × 5 × 6 × 7 = 5040

∴ 3! + 4! ≠ 7!

#### Question 3:

Compute

#### Answer:

#### Question 4:

If , find

*x*.#### Answer:

#### Question 5:

Evaluate, when

(i)

*n*= 6,*r*= 2 (ii)*n*= 9,*r*= 5#### Answer:

(i) When

*n*= 6,*r*= 2,
(ii) When

*n*= 9,*r*= 5,_{}

^{}