In each of the following questions, one term in the number series is wrong. Find the wrong term
125, 126, 124, 127, 123, 129
Answer: E
Correct answer: 129
The series should add and subtract by turns, the amount rising each time: \( 125+1=126 \), \( 126-2=124 \), \( 124+3=127 \), \( 127-4=123 \), and then \( 123+5=128 \). The last term is given as 129, so that is the wrong one.
Please log in or register to report this question.
10, 26, 74, 218, 654, 1946, 5834
Answer: D
Correct answer: 654
Each term should be three times the one before, less four: \( 3(10)-4=26 \), \( 3(26)-4=74 \), \( 3(74)-4=218 \), and then \( 3(218)-4=650 \). The series gives 654 instead, so that is the wrong one; from 650 the rule resumes with 1946 and 5834.
Please log in or register to report this question.
1, 2, 6, 15, 31, 56, 91
Answer: D
Correct answer: 91
The gaps should be the successive squares: \( 1, 4, 9, 16, 25, 36 \). They run correctly to 56, but the last step adds only 35, giving 91 where it should give \( 56 + 36 = 92 \). So 91 is the wrong term.
Please log in or register to report this question.
3, 7, 15, 39, 63, 127, 255, 511
Answer: A
Correct answer: 39
Each term should be one less than a power of two: 3, 7, 15, 31, 63, 127, 255, 511. The fourth term is given as 39 where it should be 31, so that is the wrong one.
Please log in or register to report this question.
56, 72, 90, 110, 132, 150
Answer: E
Correct answer: 150
Each term should be the product of two consecutive numbers: \( 7\cdot8=56 \), \( 8\cdot9=72 \), \( 9\cdot10=90 \), \( 10\cdot11=110 \), \( 11\cdot12=132 \), and then \( 12\cdot13=156 \). The series ends with 150 instead, so that is the wrong one.
Please log in or register to report this question.
In each of the following questions, a number series is given with one term missing. Choose the correct alternative that will continue the same pattern.
1, 4, 9, 16, 25, ?
Answer: B
Correct answer: 36
Each term is a perfect square of the counting numbers: \[ 1^2=1,\; 2^2=4,\; 3^2=9,\; 4^2=16,\; 5^2=25 \] so the next is \( 6^2 = \mathbf{36} \).
Please log in or register to report this question.
2, 3, 5, 7, 11, ?, 17
Answer: B
Correct answer: 13
The terms are the prime numbers in order - 2, 3, 5, 7, 11 - and the one that follows 11 is 13, with 17 coming after it as the series shows.
Please log in or register to report this question.
2, 5, 9, ?, 20, 27
Answer: A
Correct answer: 14
The gaps between the terms increase by one each time: \[ 5-2=3,\quad 9-5=4,\quad \_-9=5,\quad 20-\_=6,\quad 27-20=7 \] so the missing term is \( 9 + 5 = \mathbf{14} \).
Please log in or register to report this question.
20, 19, 17, ?, 10, 5
Answer: D
Correct answer: 14
The series falls by one more each time: \( -1, -2, -3, -4, -5 \). From 17 the next step subtracts 3, giving \[ 17 - 3 = \mathbf{14} \] and then \( 14 - 4 = 10 \) and \( 10 - 5 = 5 \), as shown.
Please log in or register to report this question.
77, 49, 36, 18, ?
Answer: D
Each number in the series is the product of the digits of the preceding number
Thus, \(7 \times 7 =49, 4\times9=36,..\)
\(\therefore\) The missing number \(= 1\times8=8\)
Please log in or register to report this question.
