Railway Exams (RRB) · General Intelligence & Reasoning

Series & Coding-Decoding

15 practice questions with full step-by-step solutions, plus a concept-first explainer — free, no sign-up.

Read the explainer · 7 minPractise · 15 questions

What you'll learn

Learn to hear the hidden "rhythm" behind number and letter series, convert letters into positions using the EJOTY trick, and crack coding-decoding shifts — with step-by-step worked examples built for RRB NTPC speed and accuracy.

Read Series & Coding-Decoding: Spot the Pattern, Score Fast

This chapter has

7
easy
6
medium
2
hard

Series & Coding-Decoding — solved practice questions

8 Railways General Intelligence & Reasoning questions with step-by-step solutions. Attempt each, then reveal the answer.

  1. Q1easy

    Find the next term: 2, 6, 12, 20, 30, ?

    • A40
    • B42
    • C36
    • D44
    Show answer & solution

    Correct answer: (B) 42

    The differences increase by 2 (4, 6, 8, 10), so the next difference is 12; 30 + 12 = 42.

  2. Q2easy

    Find the next term: 5, 10, 20, 40, ?

    • A60
    • B70
    • C80
    • D100
    Show answer & solution

    Correct answer: (C) 80

    Each term is double the previous one, so 40 times 2 = 80.

  3. Q3easy

    Find the next term: 1, 4, 9, 16, 25, ?

    • A30
    • B49
    • C35
    • D36
    Show answer & solution

    Correct answer: (D) 36

    These are perfect squares (1, 4, 9, 16, 25), so the next is 6 squared = 36.

  4. Q4medium

    Find the next term: 3, 6, 11, 18, 27, ?

    • A36
    • B38
    • C40
    • D39
    Show answer & solution

    Correct answer: (B) 38

    The differences are consecutive odd numbers (3, 5, 7, 9, 11), so 27 + 11 = 38.

  5. Q5medium

    Find the next term: 1, 1, 2, 3, 5, 8, ?

    • A11
    • B12
    • C13
    • D15
    Show answer & solution

    Correct answer: (C) 13

    This is the Fibonacci series; each term is the sum of the two before it, so 5 + 8 = 13.

  6. Q6easy

    Find the next term: 7, 14, 28, 56, ?

    • A98
    • B84
    • C110
    • D112
    Show answer & solution

    Correct answer: (D) 112

    Each term is double the previous one, so 56 times 2 = 112.

  7. Q7easy

    Find the next letter: A, C, E, G, ?

    • AH
    • BI
    • CJ
    • DK
    Show answer & solution

    Correct answer: (B) I

    The letters skip one each time (missing B, D, F, H), so after G comes I.

  8. Q8medium

    Find the next term: AZ, BY, CX, ?

    • ADV
    • BDW
    • CEW
    • DCW
    Show answer & solution

    Correct answer: (B) DW

    First letters move forward A, B, C, D and second letters move backward Z, Y, X, W, giving DW.

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