Prime Number Series:
Example 1. 4, 9, 25, 49, 121, 169,…
(a) 324 (b) 289
(c) 225 (d) 196
Solution. (b) The given series is a consecutive square of prime number series.
The next prime number is 289.
Example 2. 4, 8, 16, 32, 64… 256
(a) 96 (b) 98
(c) 86 (d) 106
Solution. (a) The numbers are multiplied by 2 to get the next number.
64 × 2 = 128
Example 3. 3,6,9,12,15,…. 21
(a) 16 (b) 17
(c) 20 (d) 18
Solution. (d) The difference between the numbers is 3.
15 + 3 = 18
Example 4. 5040, 720, 120, 24, ….2,1
(a) 8 (b) 7
(c) 6 (d) 5
(n2 + 1) Series
(n2 -1) Series
(n2 + n) Series
(n2 – n) Series
(n3 + 1) Series
(n3 -1) Series
(n3 + n) Series
(n3 – n) Series
Letter Series - Type 1
One Letter Series Such series consists of one letter in each term and this
series is based on increasing or decreasing positions of corresponding letters
according to English alphabet.
Example 1: B, C, A, D, Z, E, … F, X, G
(a) U (b) Y
(c) W (d) V
Solution. (b) The sequence consists of two series B, A, Z, Y, X and C, D, E, F,
G. The missing letter is Y.
Letter Series - Type 2
Two Letter Series The first letters of the series follow one logic and the
second letters follow another logic.
Example 2: EZ, DX, CV,..., AR, ZP
(a) CS (b) AM
(c) BT (d) TG
Solution. (c) First and second letters follow a sequence of-1 and -2
Letter Series - Type 3
Three Letter Series: :Such series consist of three letters in each term. The
first letters follow one logic, the second letters follow another logic and the
third letters follow some other logic.
Example 3: DIE, XCY, RWS, ...
(a) LQN (b) QMP
(c) LMS (d) LQM
Solution. (d) First, second and third letters of each group follow a sequence of
Letter Series - Type 4
A series of letters is given with one or more missing letters. From the
choices, the choice that gives the letters that go into the blanks has to be
selected as answer.
Example 4: In the following series some letters are missing. From the
choices, select the choice that gives that letters that can fill the blanks in
the given sequence.
a_ c_ b_ab_a_ca_c
(a) abaccb (b) accbab
(c) aabbcc (d) baccbb
Solution. (d) First of all, notice that there are 6 blanks in the given sequence
and each choice gives six letters to fill the six blank in order. Now, we have
to select an alternative which if placed in the blanks of the series in order,
we get a complete series of letters which follow some particular pattern.
The best way is to try with each option. Inserting the letters of option (d) in
place of the blanks, we get a series like “abc abc abc abc abc” which is a
repetition of the group of letters “abc”.
Letter Series - Type 5
Here, students are asked to count how many times a particular letter or group
of letters satisfying some conditions occurs and mark that number as the answer
Example 11: In the following sequence of letters, in how many instances the
letters n is immediately preceded by the letter t ?
(a) 5 (b) 6
(c) 7 (d) 8
Solution. (d) On counting, we find that the letter n occurs 8 times, where n is
immediately preceded by the letter t.