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

(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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