Find out the wrong term: 11, 5, 20, 12, 40, 26, 74, 54
(A) 5
(B) 20
(C) 40
(D) 26
Solution:
The given sequence is a combination of two series:I: 11, 20, 40, 74 and II: 5, 12, 26, 54The correct pattern in I: is + 9, + 18, + 36,.....So, 40 is wrong and must be replaced by (20 + 18) i.e., 38.
65.
Which term of the series 5, 8, 11, 14, ....is 320 ?
(A) 104th
(B) 105th
(C) 106th
(D) 64th
Solution:
Clearly, 5 + 3 = 8, 8 + 3 = 11, 11 + 3 = 14,................So, the series in an A.P. in which a = 5 and d = 3Let 320 be the nth term of the series.Then, 320 = 5 + (n - 1) × 3 or (n - 1) = 105 or n = 106
66.
Find out the wrong term: 1, 5, 9, 15, 25, 37, 49
(A) 9
(B) 15
(C) 25
(D) 37
Solution:
The terms of the given series are 12 , (22 + 1), 32 , (42 + 1), 52 , (62 + 1), 72 So, 15 is wrong and must be replaced by (42 + 1) i.e., 17.
67.
Find the missing term: 2, 3, 5, 7, 11, ?, 17
(A) 12
(B) 13
(C) 14
(D) 15
Solution:
Clearly, the given series consists of prime numbers starting from 2. So, the missing term is the prime number after 11, which is 13.
The given sequence is a combination of three series:I. 1st, 4th, 7th, 10th, 13th terms i.e., 2, 4, 6, 8, ?II. 2nd, 5th, 8th, 11th terms i.e., 1, 4, 7, 10III. 3rd, 6th, 9th, 12th terms i.e., 2, 5, 8, 11Clearly, I. consists of consecutive even numbers. So, the missing term is 10.
69.
Find out the wrong term: 6, 15, 35, 77, 165, 221
(A) 35
(B) 77
(C) 165
(D) 221
Solution:
The terms of the series are product of two consecutive prime numbers i.e., (2 × 3), (3 × 5), (5 × 7), (7 × 11),...........So, 165 is wrong and must be replaced by (11 × 13) i.e., 143.
70.
What will come at the place of question mark ? 6, 24, 60,120, 210, ?
(A) 336
(B) 366
(C) 330
(D) 660
Solution:
First Number = 1 *2 *3 = 6 Second Number = 2*3*4 = 24 Third Number = 3*4*5 = 60 Fourth Number = 4*5*6 = 120 Fifth Number = 5*6*7 = 210 Sixth Number = 6*7*8 = 336. Alternatively, 2*2*2-2=6 3*3*3-3=24 4*4*4-4=60 5*5*5-5=120 6*6*6-6=210 7*7*7-7=336.