Series Completion Questions and Answers

Q: 6, 11, 21, 36, 56, ?

Correct answer: 81The gaps rise by five each time: \( 11-6=5 \), \( 21-11=10 \), \( 36-21=15 \), \( 56-36=20 \). The next gap is 25, giving \[ 56 + 25 = \mathbf{81} \]

Q: 1, 6, 13, 22, 33, ?

Correct answer: 46The gaps are the successive odd numbers from five: \( 5, 7, 9, 11 \). The next gap is 13, so \[ 33 + 13 = \mathbf{46} \]

Q: 1, 1, 2, 6, 24, ?, 720

Correct answer: 120The terms are the factorials: \( 0!=1,\; 1!=1,\; 2!=2,\; 3!=6,\; 4!=24 \), so the missing one is \( 5! = \mathbf{120} \), followed by \( 6! = 720 \).

Q: 2,15,41,80,?

Correct answer: 132The gaps are multiples of thirteen: \( 15-2=13 \), \( 41-15=26 \), \( 80-41=39 \). The next gap is \( 52 \), giving \[ 80 + 52 = \mathbf{132} \]

Q: 6, 11, 21, 36, 56, ?

Correct answer: 81The gaps rise by five each time: \( 11-6=5 \), \( 21-11=10 \), \( 36-21=15 \), \( 56-36=20 \). The next gap is 25, giving \[ 56 + 25 = \mathbf{81} \]

Q: 563, 647, 479, 815, ?

Correct answer: 143The steps alternate in sign and double each time: \( +84 \), \( -168 \), \( +336 \), so the next is \( -672 \): \[ 815 - 672 = \mathbf{143} \]

Important Instructions

Direction for [ Question No: 11 To 20 ] :

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.

11.

21, 25, 33, 49, 81, ?

A.144
B.145
C.129
D.113
E.97

Answer: B

The pattern is \(+2^2, +2^3, +2^4, +2^5,...\)

\(\therefore\) Missing number = \(81+2^6 = 81+64=145.\)

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12.

6, 11, 21, 36, 56, ?

A.42
B.51
C.81
D.71
E.76

Answer: C

Correct answer: 81

The gaps rise by five each time: \( 11-6=5 \), \( 21-11=10 \), \( 36-21=15 \), \( 56-36=20 \). The next gap is 25, giving \[ 56 + 25 = \mathbf{81} \]

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13.

3, 6, 18, 72, ?

A.144
B.216
C.256
D.288
E.360

Answer: E

The pattern is \(\times 2, \times 3, \times 4,...\)

\(\therefore\) Missing number \(=72\times5=360\).

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14.

1, 6, 13, 22, 33, ?

A.42
B.44
C.45
D.46
E.47

Answer: D

Correct answer: 46

The gaps are the successive odd numbers from five: \( 5, 7, 9, 11 \). The next gap is 13, so \[ 33 + 13 = \mathbf{46} \]

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15.

1, 2, 3, 6, 9, 18, 34, ?

A.25
B.27
C.36
D.48
E.81

Answer: B

The numbers are alternately multiplied bt \(2\) and \(\frac{3}{2}\).
Thus \(1\times2=2,2\times \frac{3}{2}=3, 3\times 2=6,6\times \frac{3}{2}=9,..\)

\(\therefore\) Missing number = \(18 \times \frac{3}{2}=27\).

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16.

19, 2, 38, 3, 114, 4, ?

A.214
B.228
C.256
D.352
E.456

Answer: E

The sequence is a combination of two series :
i. 19, 38, 114, ? and ii. 2, 3, 4
The pattern followed in i is \(\times2,\times3,...\)

\(\therefore\) Missing number \(=114\times4=456\)

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17.

1, 1, 2, 6, 24, ?, 720

A.100
B.104
C.108
D.120
E.124

Answer: D

Correct answer: 120

The terms are the factorials: \( 0!=1,\; 1!=1,\; 2!=2,\; 3!=6,\; 4!=24 \), so the missing one is \( 5! = \mathbf{120} \), followed by \( 6! = 720 \).