Series: The Well Arranged order of Number/letter placed in a special group is called series.
Series completion deals with questions in which series of numbers or alphabetical letters are given, which are generally called as terms of the series. These terms follow a certain pattern throughout. The candidate is required to recognize this pattern and either complete the given series with the most suitable alternative or find wrong in the series.

The Questions from these chapter can classified into three groups:


1. Number Series:

TYPE1: Completing the Series: 
A Number Series will be given with one term missing, We have to choose the correct alternative that will continue the same pattern and fill in the blank Space.


Example 1: 1, 4, 9, 16, 25, ?

a) 35

b) 36

c) 48

d) 49

Solution: (b) 36, As Given series is of Perfect Squares

Example 2: 2, 3, 5, 7, 11, (...), 17

a) 12

b) 13

c) 14

d) 15

Solution: (b) Consecutive Prime Numbers are given in the Series. After 11 next Prime Number is 13.

TYPE2: Picking the Wrong Element:
A Number Series will be given, one number in the number series will be wrong. We have to figure out the wrong term.


Example1: 1, 4, 9, 16, 25, 37, 49

a) 16

b) 9

c) 25

d) 37

Solution: (d) The series is of Perfect Squares but 37 is not a Perfect Square

Example2: 1, 8, 27, 64, 125, 224, 343
a) 224
b) 343
c) 64
d) 27
Solution: (a) The Series of Cubes of 13, 23, 33, 43, 53, 63, 7But 224 is not cube of 6.

2. Alphabet Series:

Various term of a letter series will be given with one term missing. We have to choose the missing term out of the given alternatives.


Example1: BEH, KNQ, TWZ,?
a) IJK
b) CFI
c) BDF
d) ADG
Solution: (b) The Series can written in 3 Part
1   B(2) + 9        K(11)    +9     T(20) +9   C(3)
2   E(5) + 9        N(14)    +9    W(23) +9   F(6)
3   H(8) + 9       Q(17)    +9     Z(26) +9   I(9)
Example2: U, O, I, ? ,W
a) E
b) C
c) S
d) G
Solution: (b) U(21)-6=> O(15)-6=> I(9)-6=> C(3)-6=> W(23)

3. Letter Series:

In letter series, some of the letters are missing which are given in that order as one of the alternative. We have to choose the alternative which complete the series.


Example1:  a_bbc_aab_cca_bbcc
a) bacb
b) acba
c) abba
d) caba
Solution: (b) The Pattern is aabbcc
Example2: a_bc_c_abb_bca_
a) cccbc
b) cbbac
c) accba
d) abbba
Solution: (c) Pattern is aabcc ccabb bbcaa