Introduction
In a Series a number of objects or arranged or coming one other in succession. Series is simply adding the terms in a sequence. An arithmetic series involves adding the terms of an arithmetic sequence and a geometric series involves adding the terms of a geometric sequence.
NUMBER SERIES
In this type of series, the set of given numbers in a series are related to one another in a particular pattern or manner. The relationship between the numbers maybe
(i) consecutive odd/even numbers,
(ii) Consecutive prime numbers,
(iii) Squares/cubes of some numbers with/without variation of addition or subtraction of some number,
(iv) Sum/product/difference of preceding number(s),
(v) Addition/subtraction/multiplication/division by some number, and
(vi) Many more combinations of the relationships given above.
EXAMPLE 1:
Find the missing term in the following sequence.
5,11,24,51,106.......................
Sol. Double the number and then add to it
1,2,3,4 etc.
Thus the next term is \[2\times 106+5=217.\]
EXAMPLE 2:
Complete the series 4, 9, 16, 25...........
(a) 32 (b) 42
(c) 55 (d) 36
Sol. (d) Each number is a whole square.
EXAMPLES 3:
Find the wrong term in the series 3, 8, 15, 24,34,48,63.
(a) 15 (b) 12
(c) 34 (d) 63
Sol. (c) \[8-3=5\]
\[15-8=7\]
\[24-15=9\]
\[34-24=10\]
\[48-34=14\]
\[63-48=15\]
Obviously difference should be 11 & 13 instead of 10 & 14. Therefore, 34 is the wrong term.
EXAMPLES 4:
Complete the given series 4, 9,13,22,35..........
(a) 57 (b) 70
(c) 63 (d) 75
Sol. (a) \[4+9=13, 13+9=22\] etc.
EXAMPLES 5:
Complete the given series 66, 36, 18...........
(a) 9 (b) 3
(c) 6 (d) 8
Sol. (d) \[6\times 6=36;3\times 6=18;1\times 8=8.\]
EXAMPLE 6:
Complete the given series 61, 67,71,73,79,...
(a) 81 (b) 82
(c) 83 (d) 85
Sol. (c) Prime number series. 83 is the next prime number.
EXAMPLE 7:
Complete the given series 8, 24, 12,36,18,54,
(a) 27 (b) 29
(c) 31 (d) 32
Sol. (I) Multiply by 3 and divide the result by 2.
Next term is \[\frac{54}{2}=27\]
ALPHABET SERIES
In this type of question, a series of single, pairs or groups of letters or combinations of letters and numbers is given. The terms of the series form a certain pattern as regards the position of the letters in the English alphabet.
In the following questions, various terms of a letter series are given with one term missing as shown. Choose the missing term out of the options.
EXAMPLES 8:
AZ, GT.MN,...........,YB
(a) KF (b) RX
(c) SH (d) TS
Sol. (c) The logic is+6 and-6.
EXAMPLE 9:
Choose the missing term from the given options.
KM5, 1P8, GS11, EV14,
(a) BX17 (b) BY17
(c) CY18 (d) CY17
Sol. (d) Logic for the letters is -2, +3 steps, numbers added is 3.
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