Page 33 - Mathematics Class - X

Viva-Voce

1. What will be the sum of first “s” odd numbers?
Ans. The sum of first “s” odd numbers is s .
2
2. Find the sum of all odd numbers between 7 and 27.
Ans. The odd numbers are 9, 11, 13, 15, 17, 19, 21, 23, 25
n
Sn = [2a + (n – 1)d] Here, a = 9, d = 2 and n = 9
2
9
= [2× 9 + (9 – 1)2]
2
9
= [18 + 16]
2
= 153

3. Is the common difference between two consecutive odd numbers same as in two consecutive even numbers?
Ans. Yes
4. Can you find the largest odd number? Why or Why not?

Ans. No, we cannot find the largest odd number as it is an infinite set.
5. How do we represent a set of natural numbers?

Ans. A set of natural numbers is represented by a letter “N”, N = {1,2,3,4, .....}

MCQs

1. Which term of the A.P. 24, 21, 18, ... is the first negative term?
a) 8 b) 9 c) 10 d) 12 th
th
th
th
2. The sum of first five multiples of 3 is
a) 45 b) 65 c) 75 d) 90
3. For an A.P. if a – a = 45, then d equals to
25
20
a) 9 b) –9 c) 18 d) 23
4. 15th term of the A.P. x – 7, x – 2, x + 3, ..... is

a) x + 63 b) x + 83 c) x + 73 d) x + 53
5. 1 + (1 + 1) + (1 + 1 + 1) + ...... + (1 + 1 + 1 + 1 + ...... (n – 1) times) = ?
a) n(n + 1)/2 b) (n – 1)n/2 c) n 2 d) n

Answers: 1. c) 10 2. a) 45 3. a) 9 4. a) x + 63 5. b) (n – 1)n/2
th

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