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 ![](https://img-nm.mnimgs.com/img/study_content/curr/1/11/11/167/4211/chapter%207_html_350ec2ad.gif)
![](https://img-nm.mnimgs.com/img/study_content/curr/1/11/11/167/4211/chapter%207_html_350ec2ad.gif)
Answer:
![](https://img-nm.mnimgs.com/img/study_content/curr/1/11/11/167/4211/chapter%207_html_8d46127.gif)
Question 4:
If
, find x.
![](https://img-nm.mnimgs.com/img/study_content/curr/1/11/11/167/4212/chapter%207_html_329ae33a.gif)
Answer:
![](https://img-nm.mnimgs.com/img/study_content/curr/1/11/11/167/4212/chapter%207_html_58a92582.gif)
Question 5:
Evaluate
, when
![](https://img-nm.mnimgs.com/img/study_content/curr/1/11/11/167/4213/chapter%207_html_m3aadba17.gif)
(i) n = 6, r = 2 (ii) n = 9, r = 5
Answer:
(i) When n = 6, r = 2, ![](https://img-nm.mnimgs.com/img/study_content/curr/1/11/11/167/4213/chapter%207_html_3f6b0689.gif)
![](https://img-nm.mnimgs.com/img/study_content/curr/1/11/11/167/4213/chapter%207_html_3f6b0689.gif)
(ii) When n = 9, r = 5, ![](https://img-nm.mnimgs.com/img/study_content/curr/1/11/11/167/4213/chapter%207_html_m76bcd6e3.gif)
![](https://img-nm.mnimgs.com/img/study_content/curr/1/11/11/167/4213/chapter%207_html_m76bcd6e3.gif)
![](https://img-nm.mnimgs.com/img/study_content/curr/1/11/11/167/4213/chapter%207_html_17e8376c.gif)