Logical Reasoning - Series Completion

Series Completion Description

In a series completion questions, a series is given, with one letter/number missing. In order to complete the series it is important to choose the correct alternative from the given ones that will complete the series.

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: P, U, Z, … J, 0, T
(a) E (b) U (c) S (d) P
Solution. (a) The sequence is P+ 5, U+ 5,Z+ 5. The missing letter is Z + 5 = E

2.Two Letter Series:- The first letters of the series follow one logic and the second letters follow another logic.
Example: DG, HK, LO, PS, TW,…
(a) XA (b) ZA (c) XB (d) None of these
Solution. (a) First and second letters follow a sequence of + 4.

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: VPG, UQF, ..., SSD, RTC
(a) SQD (b) TRE (c) TRS (d) QDT
Solution. (b) First, second and third letters follow a sequence of –1, + 1, –1 series respectively.

4. More Letters:- 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: 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”.

5. Letters Occurence:- 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 choice.
Example: In the following sequence of letters, in how many instances the letters n is immediately preceded by the letter t ?
s n r u a t n n g h j t k n s t n d g c l n t t t n n n t n t n t s m v b t n g c x d p t n k l s t n 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. 
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