Series Aptitude basics, practice questions, answers and explanations 
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Introduction: In series, words, letters or digits are given in a specific sequence/ order and you are asked to find out the next word, letter or digit to complete the given series. Numbers or alphabetical letters are generally called as terms of the series. These terms follow a certain pattern throughout.

Numbers Series

In the number series, some numbers are arranged in a particular sequence. All the , numbers form a series and change in a certain order.

The number itself may be

- Perfect Square
Eg: 4,9,16,25,36,……..
Ans: 49

- Perfect Cube
Eg: 1,8,27,64,125,……
Ans: 216

- Prime
Eg: 1,2,3,5,7………
Ans: 11

- Combination
Eg: 2,5,10,17,26……
Ans: 37 

Alphabet Seiries

Another type of number series question involves the substitution of letters of the alphabet to numbers. For example A=1, B=2,C=3 etc. It may seem strange to consider these as number series questions but they do actually work in exactly the same way after substitution.

Eg: 1. D, G, J, M…….
Ans: P

2.C, X, D, W,….
Ans: E

3.S, U, W, Y,....
Ans: A


Exercise Questions


1) DEF, DEF2, DE2F2, _____, D2E2F3

a) DEF3 
b) D3EF3 
c) D2E3F 
d) D2E2F2
Answer: Option d
Explanation: In this series, the letters remain the same: DEF. The subscript numbers follow this series:
111, 112, 122, 222, 223, 233, 333, ...


2) DKY FJW HIU JHS ——

a) KGR 
b) LFQ 
c) KFR 
d)LGQ 
Answer:d
Explanation : 1st letter = +2 ( D+ 2 = F)
2nd letter = -1 (K –1 = J)
3rd letter = -2 (Y-2 = W)


3) 101 131 374 383 313 727

a)383 
b)374 
c)101 
d)727 
Answer: b
Explanation : 374 (palindrome)


4) 380, 188, 92, 48, 20, 8, 2

a) 188 
b) 92 
c) 48 
d) 20 
Answer: c
Explanation : Wrong no. = 48, Correct no. = 44
Each term will be four more than two times the next term


5) 8 12 21 30 46 _____

a)54 
b)62 
c)50 
d)34 
Answer: b
Explanation: 2*2+4=4+4=8, 2*2+8=4+8=12, 3*3+12=9+12=21 , 3*3+21=9+21=30, 
4*4+30=16+30=46, 4*4+46=16+46=62

6) 19 23 29 31 37 41 _______

a)43 
b)47 
c)53 
d)51
Answer: a
Explanation : Numbers are all primes. The next prime is 43.