Tips on cracking Reasoning Questions Related To Number Series

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3 Tips on Solving Reasoning Questions on Number
Series
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Tip 1 Arithmetic Series, Geometric Series,
Patterns in Differences
(1) Arithmetic Series When the differences
between the successive numbers given in the
series is the same. For example 2, 5, 8, 11,
14... (here the difference between the numbers is
3, hence the next number will be 17) (2)
Geometric Series When each successive number in
the series is obtained by multiplying or
dividing the previous one by a fixed number. For
example 2, 6, 18, 72, (3) Patterns in
differences Calculate the differences between
the numbers given in the series provided in the
question. Then try to observe the pattern in the
new set of numbers that you have obtained after
taking out the difference. Question Look at
this series V, VIII, XI, XIV, __, XX, ... What
number should fill the blank? Solution This is
an arithmetic series in Roman numerals each no.
is 3 more than the previous one. Thus, the
missing number will be the Roman equivalent of 20
3 17, i.e., XVII. Question Look at this
series 201, 202, 204, 207, ... What number
should come next? Solution The difference
between the successive numbers is 1, 2, 3
respectively. Thus, the difference keeps on
increasing by 1. Thus, the next number in the
series will be 207 4 211.
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Tip 2 Pattern in Alternate/Adjacent numbers

• Pattern in Alternate numbers When there is a
  pattern between every alternate or third number
  in the series. For example 2, 9, 5, 12, 8 , 15,
  11....
• (2) Pattern in adjacent number When adjacent
  numbers in the series changes based on a logical
  pattern. For example 2, 4, 12, 48... Here the
  numbers are being multiplied by 2, then by 3,
  then by 4 etc.
• Question Look at this series F2, __, D8, C16,
  B32, ... What number should fill the blank?
• Solution
• This is a complex series in which the successive
  letters decrease by 1 and the successive numbers
  are multiplied by 2. Thus, the number in the
  blank will be E4.
• Question Look carefully at the following series
  and choose the pair that comes next.
• 42 40 38 35 33 31 28
• A. 25 22 B. 26 23 C. 26 24 D. 25 23
• Solution
• This is an alternating subtraction series in
  which 2 is subtracted twice, then 3 is subtracted
  once, then 2 is subtracted twice, and so on. So
  the next terms in the following series will be 26
  and 24. Thus the correct answer is C.

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Tip 3 Prime Numbers, Squares/Cubes, Alternate
primes/exponents
(1) Squares/Cubes When numbers are a series
of perfect squares. For example 81, 100, 121,
144, 169... (2) Cube/Square roots When the
numbers are a series of perfect cubes. For
example 512, 729, 1000... (3) Alternate
Primes Here the series is framed by taking
the alternative prime numbers. For example 2, 5,
11, 17, 23, 31 Question Look at this series 4,
7, 16, 13, __, 19, 64, 29, ... What number should
fill the blank? Solution There are two
alternating series here. The first one is the
square of the multiples of 2 22, 42, 62, 82
and the second one is a series of alternating
prime numbers. The missing number is a part of
the first series so the missing number is 62
36. Question Look carefully at the following
series and choose the pair that comes next. 4
7 26 10 13 20 16 A. 14 17 B. 18 14
C. 19 13 D. 19 14 Solution Two patterns
alternate here, with every third number following
the alternate pattern. In the main series,
beginning with 4, 3 is added to each number to
arrive at the next. In the alternating series,
beginning with 26, 6 is subtracted from each
number to arrive at the next. So the next numbers
will be 16 3 19, 20 6 14. Thus, the
correct answer is D.
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