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

Rajasthan Board RBSE Solutions for Class 11 Maths Chapter 7 Permutations and Combinations Ex 7.2 Textbook Exercise Questions and Answers.

RBSE Class 11 Maths Solutions Chapter 7 Permutations and Combinations Ex 7.2

Question 1.
Evaluate
(i) 8! 
(ii) 4! - 3!
Answer:
(i) 8! = 8 × 7 × 6 × 5 × 4 × 3 × 2 × 1
= 40320

(ii) 4! - 3! = (4 × 3 × 2 × 1) - (3 × 2 × 1)
= 24 - 6 
= 18

Question 2.
Is 3! + 4! = 7!?
Answer:
L.H.S. = 3! + 4! 
= 3 × 2 × 1 + 4 × 3 × 2 × 1
= 6 + 24
= 30 
and R.H.S. = 7! = 7 × 6 × 5 × 4 × 3 × 2 × 1
= 5040
L.H.S. ≠ R.H.S.
Thus 3! + 4! = 7! is not true.

Question 3.
Compute: \(\frac{8 !}{6 ! \times 2 !}\).
Answer:

Question 4.
If \(\frac{1}{6 !}+\frac{1}{7 !}=\frac{x}{8 !}\), find x.
Answer:

or x = 8 × 8 = 64
Thus, x = 64

Question 5.
Evaluate \(\frac{n !}{(n-r) !}\) when:
(i) n = 6, r = 2
(ii) n = 9, r = 5
Answer:
(i) n = 6, r = 2

(ii) n = 9, r = 5