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RD Sharma Class 11 Solutions Chapter - Permutations | Mathematics (Maths) Class 11 - Commerce PDF Download

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16. Permutations
Exercise 16.1
1. Question
Compute
(i) 
(ii) 
(iii). L.C.M. (6!, 7!, 8!)
Answer
i. Given 
= 30 × 29
= 870
ii. Given 
We know that:
11! = 11 × 10 × 9 × … × 1
10! = 10 × 9 × 8 × … × 1
9! = 9 × 8 × 7 × … × 1
Putting these values, we get,
= 110 – 10
Hence, 
iii. We have to find LCM of 6!, 7!, and 8!
We can write as,
= 8! = 8 × 7 × 6!
= 7! = 7 × 6!
= 6! = 6!
Therefore,
L.C.M (6!, 7!, 8!) = LCM [8 × 7 × 6!, 7 × 6!, 6! ]
= 8 × 7 × 6!
Hence, LCM is 8!
Page 2


16. Permutations
Exercise 16.1
1. Question
Compute
(i) 
(ii) 
(iii). L.C.M. (6!, 7!, 8!)
Answer
i. Given 
= 30 × 29
= 870
ii. Given 
We know that:
11! = 11 × 10 × 9 × … × 1
10! = 10 × 9 × 8 × … × 1
9! = 9 × 8 × 7 × … × 1
Putting these values, we get,
= 110 – 10
Hence, 
iii. We have to find LCM of 6!, 7!, and 8!
We can write as,
= 8! = 8 × 7 × 6!
= 7! = 7 × 6!
= 6! = 6!
Therefore,
L.C.M (6!, 7!, 8!) = LCM [8 × 7 × 6!, 7 × 6!, 6! ]
= 8 × 7 × 6!
Hence, LCM is 8!
2. Question
Prove that 
Answer
Given: 
L.H.S 
Hence, L.H.S = R.H.S
3 A. Question
Find x in each of the following :
Answer
We have 
We know that
5! = 5 × 4 × 3 × 2 × 1
6! = 6 × 5 × 4 × 3 × 2 × 1
Hence, x = 36
3 B. Question
Find x in each of the following :
Answer
Page 3


16. Permutations
Exercise 16.1
1. Question
Compute
(i) 
(ii) 
(iii). L.C.M. (6!, 7!, 8!)
Answer
i. Given 
= 30 × 29
= 870
ii. Given 
We know that:
11! = 11 × 10 × 9 × … × 1
10! = 10 × 9 × 8 × … × 1
9! = 9 × 8 × 7 × … × 1
Putting these values, we get,
= 110 – 10
Hence, 
iii. We have to find LCM of 6!, 7!, and 8!
We can write as,
= 8! = 8 × 7 × 6!
= 7! = 7 × 6!
= 6! = 6!
Therefore,
L.C.M (6!, 7!, 8!) = LCM [8 × 7 × 6!, 7 × 6!, 6! ]
= 8 × 7 × 6!
Hence, LCM is 8!
2. Question
Prove that 
Answer
Given: 
L.H.S 
Hence, L.H.S = R.H.S
3 A. Question
Find x in each of the following :
Answer
We have 
We know that
5! = 5 × 4 × 3 × 2 × 1
6! = 6 × 5 × 4 × 3 × 2 × 1
Hence, x = 36
3 B. Question
Find x in each of the following :
Answer
We have 
We can write as
10! = 10 × 9!
9! = 9 × 8!
By putting these values
Hence, x = 100
3 C. Question
Find x in each of the following :
Answer
We have 
We can write as.
8! = 8 × 7 × 6!
7! = 7 × 6!
Putting the value, we get
Hence, x = 64
4 A. Question
Page 4


16. Permutations
Exercise 16.1
1. Question
Compute
(i) 
(ii) 
(iii). L.C.M. (6!, 7!, 8!)
Answer
i. Given 
= 30 × 29
= 870
ii. Given 
We know that:
11! = 11 × 10 × 9 × … × 1
10! = 10 × 9 × 8 × … × 1
9! = 9 × 8 × 7 × … × 1
Putting these values, we get,
= 110 – 10
Hence, 
iii. We have to find LCM of 6!, 7!, and 8!
We can write as,
= 8! = 8 × 7 × 6!
= 7! = 7 × 6!
= 6! = 6!
Therefore,
L.C.M (6!, 7!, 8!) = LCM [8 × 7 × 6!, 7 × 6!, 6! ]
= 8 × 7 × 6!
Hence, LCM is 8!
2. Question
Prove that 
Answer
Given: 
L.H.S 
Hence, L.H.S = R.H.S
3 A. Question
Find x in each of the following :
Answer
We have 
We know that
5! = 5 × 4 × 3 × 2 × 1
6! = 6 × 5 × 4 × 3 × 2 × 1
Hence, x = 36
3 B. Question
Find x in each of the following :
Answer
We have 
We can write as
10! = 10 × 9!
9! = 9 × 8!
By putting these values
Hence, x = 100
3 C. Question
Find x in each of the following :
Answer
We have 
We can write as.
8! = 8 × 7 × 6!
7! = 7 × 6!
Putting the value, we get
Hence, x = 64
4 A. Question
Convert the following products into factorials :
5 · 6 · 7 · 8 · 9 · 10
Answer
Given 5 . 6 . 7 . 8 . 9 . 10
Find: Convert into Factorial
Now, We can write as
= 
Hence, 
4 B. Question
Convert the following products into factorials :
3 · 6 · 9 · 12 · 15 · 18
Answer
Given 3 . 6 . 9 . 12 . 15 . 18
Find: Convert into Factorial
= (3 × 1) × (3 × 2) × (3 × 3) × (3 × 4) × (3 × 5) × (3 × 6)
= 3
6
 (1 × 2 × 3 × 4 × 5 × 6)
= 3
6
 (6!)
4 C. Question
Convert the following products into factorials :
(n + 1)(n + 2) (n + 3) …(2n)
Answer
Given (n + 1)(n + 2) (n + 3) …(2n)
Find: Convert into Factorial
4 D. Question
Convert the following products into factorials :
1 · 3 · 5 · 7 · 9 …(2n – 1)
Answer
Given 1 · 3 · 5 · 7 · 9 …(2n – 1)
Find: Convert into Factorial
Page 5


16. Permutations
Exercise 16.1
1. Question
Compute
(i) 
(ii) 
(iii). L.C.M. (6!, 7!, 8!)
Answer
i. Given 
= 30 × 29
= 870
ii. Given 
We know that:
11! = 11 × 10 × 9 × … × 1
10! = 10 × 9 × 8 × … × 1
9! = 9 × 8 × 7 × … × 1
Putting these values, we get,
= 110 – 10
Hence, 
iii. We have to find LCM of 6!, 7!, and 8!
We can write as,
= 8! = 8 × 7 × 6!
= 7! = 7 × 6!
= 6! = 6!
Therefore,
L.C.M (6!, 7!, 8!) = LCM [8 × 7 × 6!, 7 × 6!, 6! ]
= 8 × 7 × 6!
Hence, LCM is 8!
2. Question
Prove that 
Answer
Given: 
L.H.S 
Hence, L.H.S = R.H.S
3 A. Question
Find x in each of the following :
Answer
We have 
We know that
5! = 5 × 4 × 3 × 2 × 1
6! = 6 × 5 × 4 × 3 × 2 × 1
Hence, x = 36
3 B. Question
Find x in each of the following :
Answer
We have 
We can write as
10! = 10 × 9!
9! = 9 × 8!
By putting these values
Hence, x = 100
3 C. Question
Find x in each of the following :
Answer
We have 
We can write as.
8! = 8 × 7 × 6!
7! = 7 × 6!
Putting the value, we get
Hence, x = 64
4 A. Question
Convert the following products into factorials :
5 · 6 · 7 · 8 · 9 · 10
Answer
Given 5 . 6 . 7 . 8 . 9 . 10
Find: Convert into Factorial
Now, We can write as
= 
Hence, 
4 B. Question
Convert the following products into factorials :
3 · 6 · 9 · 12 · 15 · 18
Answer
Given 3 . 6 . 9 . 12 . 15 . 18
Find: Convert into Factorial
= (3 × 1) × (3 × 2) × (3 × 3) × (3 × 4) × (3 × 5) × (3 × 6)
= 3
6
 (1 × 2 × 3 × 4 × 5 × 6)
= 3
6
 (6!)
4 C. Question
Convert the following products into factorials :
(n + 1)(n + 2) (n + 3) …(2n)
Answer
Given (n + 1)(n + 2) (n + 3) …(2n)
Find: Convert into Factorial
4 D. Question
Convert the following products into factorials :
1 · 3 · 5 · 7 · 9 …(2n – 1)
Answer
Given 1 · 3 · 5 · 7 · 9 …(2n – 1)
Find: Convert into Factorial
= 
5 A. Question
Which of the following are true :
(2 + 3)! = 2! + 3!
Answer
Given: (2 + 3)! = 2! + 3!
L.H.S = (2 + 3)!
= 5!
R.H.S = 2! + 3!
= (2 × 1) + (3 × 2 × 1)
= 2 + 6
= 8
Hence, L.H.S ? R.H.S
5 B. Question
Which of the following are true :
(2 × 3)! = 2! × 3!
Answer
Given: (2 × 3)! = 2! × 3!
L.H.S = (2 × 3)!
= 6!
= 6 × 5 × 4 × 3 × 2 × 1
= 720
R.H.S = 2! × 3!
= 2 × 1 × 3 × 2 × 1
= 12
Hence, L.H.S ? R.H.S
6. Question
Prove that: n! (n + 2) = n! + (n + 1)!
Answer
Given: n! (n + 2) = n! + (n + 1)!
R.H.S. = n! + (n + 1)!
= n! + (n + 1)(n + 1 – 1)!
= n! + (n + 1)n!
= n!(1 + n + 1)
= n! (n + 2) = L.H.S
L.H.S = R.H.S
Hence, Proved.
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