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NCERT Solutions for class 11 Maths | Chapter 9 - Sequences and Series

Questions
1 a, b, c Î R+ and from an A.P. if abc = 4, then the minimum value of b is
A (2)2/3
B (2)1/3
C (4)2/3
D None of these

Answer:(2)2/3
2 If Sn = nP + where Sn denotes the sum of the first ‘n’ terms of an A.P. then the common difference is
A P + Q
B 2P + 3Q
C 2Q
D Q

Answer:Q
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3 If Sn = , then Sn is equal to
A 2n – (n + 1)
B n × (n + 1)/2
C (n2 + 3n + 2)/6
D n – 1 + (1/2n)

Answer:n – 1 + (1/2n)
4 The numbers 1, 4, 16 can be three terms (not necessarily consecutive) of
A No A.P.
B Only 1 or 2 G.Ps
C Infinite number of A.Ps
D Infinite number of G.Ps

Answer:Infinite number of A.Ps
5 2¹ + 2² +2³ +….+2 =
A 2(2n - 1) 2
B 2(2n-1 -1) 3
C 2(2n+1 -1)
D None of Above

Answer: 2(2n - 1) 2
6 The arithmetic mean between 2+√(2) and 2-√(2) is
A 2
B √(2)
C 0
D 4

Answer:2
7 The common difference of the sequence 5,8,11,14,… is
A 3
B −3
C 0
D 1

Answer:3
8 If A, G, H are arithmetic, geometric and harmonic means between a and b respectively, then A,G,H are
A in G.P
B in A.P
C in H.P
D Real numbers

Answer:in G.P
9 G1,G2,…,Gn are said to be n geometric means between a and b if a,G1,…Gn,b is
A a sequence
B not a sequence
C G.P
D A.P

Answer:G.P
10 The A.M between 3√(5) and 5√(5) is
A √(5)
B 2√(5)
C 3√(5)
D 4√(5)

Answer:4√(5)
11 If 2/3, k, 5/8 are in AP then the value of k is
A 31/24
B 31/48
C 24/31
D 48/31

Answer:31/48
12 If Sn = n3 + n2 + n + 1, where Sn denotes the sum of the first n terms of a series and Tm = 291, then m =
A 40
B 41
C 42
D 43

Answer:42
13 3, 5, 7, 9, ........ is an example of
A Geometric Series
B Arithmetic Series
C Rational Exponent
D Logarithm

Answer:Arithmetic Series
14 An arithmetic sequence has its 5th term equal to 22 and its 15th term equal to 62. Then its 100th term is equal to
A 410
B 408
C 406
D 404

Answer:406
15 If a, b and c are in GP then
A b = ac
B b2 = ac
C b2 = 2ac
D 2b2 = ac

Answer:b2 = ac
16 If 1/(b + c), 1/(c + a), 1/(a + b) are in AP then
A a, b, c are in AP
B a2 , b2 , c2 are in AP
C 1/1, 1/b, 1/c are in AP
D None of these

Answer:a2 , b2 , c2 are in AP
17 If a1,a2, ..... an are positive real numbers whose product is a fixed number c, then the minimum valu of a1 + a2 + ... + an-1 + 2an is 
A n (2c)1/n 
B (n + 1)c1/n
C 2n c1/n 
D (n+1)(2c)1/n

Answer:n (2c)1/n 
18 If the nth term of an AP is 3n - 4, the 10th term of AP is
A 12
B 22
C 28
D 30

Answer:28
19 If x, y, z are in GP and ax = by = cz then the value of logb a * logb c is
A 0
B 1
C -1
D None of these

Answer:1
20 Let a, b, c form a GP of common ratio r with 0 < r < 1. If a, 2b, 3c form an AP, then r equals
A 1/2
B 1/3
C 2/3
D None of these

Answer:1/3

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