NCERT solution class 11 chapter 7 Permutations and Combinations exercise 7.2 mathematics

EXERCISE 7.2

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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, 

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