Page 51 - Mathematics Class - XI

Viva-Voce

1. What does a notation n! represent?
Ans. The notation n! represents the product of first n natural numbers, i.e., the product 1 × 2 × 3 × ... × (n – 1) × n
is denoted as n!
2. From a group of 4 people, 2 are selected to form a committee. How many combinations are there?

Ans. Here, C = 4! = 1 234×× × = 6
4
2 ( 42 2)!!− 12 12×× ×
3. What is meant by combination?
Ans. A combination is a selection or all or part of a set of objects, without regard to the order in which objects
are selected.

4. What is the value of O!
Ans. 1
5. What is meant by permutation?

Ans. A permutation is an arrangement of all or part of a set of objects, with regard to the order of the arrangement.

MCQs

1. If C = C and r ≠ 9, then r = ?
14
14
r 9
a) 2 b) 5 c) 23 d) 126
2. If C = C then n = ?
n
n
30 4
a) 30 b) 4 c) 34 d) 26
3. If C = 15, then n = ?
n
n – 4
a) 5 b) 6 c) 7 d) 8
4. There are 44 diagonals in a polygon then its sides are equal to
a) 9 b) 8 c) 7 d) 11
5. If P = 12 P , then the value of n is
n
n
4
5
a) 12 b) 14 c) 16 d) 18
6. The value of 8! is equal to
7!
a) 7 b) 8 c) 56 d) None of these

7. If 1 1 x , then x = ?
4! 5! 6!
a) 6 b) 36 c) 12 d) 30

Answers: 1. b) 5 2. c) 34 3. a) 5 4. d) 11 5. c) 16 6. b) 8 7. a) 6

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