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Logical Reasoning Test Practice Course: Number and letter series

Untimed topic quiz: 18 questions on Number and letter series, with an explanation after each answer. Questions and answers are shuffled every time.

  • Course
  • Canada
  • 99 questions
  • Checked October 13, 2026
  • Fact-checked October 13, 2026
Start with the lessonsLogical Reasoning Course: Lessons: about 180 minutes of reading. Every test question is covered in the lessons.

Topic quiz 2: Number and letter series

  1. Question 1 of 18

    What number comes next in the series 4, 9, 14, 19, ?
    Show answer

    Answer: D. 24

    Each number is 5 more than the one before: 19 + 5 = 24.

  2. Question 2 of 18

    What number comes next in the series 3, 6, 12, 24, ?
    Show answer

    Answer: A. 48

    Each number is double the one before: 24 × 2 = 48.

  3. Question 3 of 18

    What number comes next in the series 81, 72, 63, 54, ?
    Show answer

    Answer: D. 45

    Each number is 9 less than the one before: 54 − 9 = 45.

  4. Question 4 of 18

    What letter comes next in the series A, C, E, G, ?
    Show answer

    Answer: D. I

    The letters skip one each time: A(1), C(3), E(5), G(7), so next is position 9, which is I.

  5. Question 5 of 18

    What number comes next in the series 1, 4, 9, 16, 25, ?
    Show answer

    Answer: D. 36

    These are square numbers: 1×1, 2×2, 3×3, 4×4, 5×5. Next is 6 × 6 = 36.

  6. Question 6 of 18

    What letter comes next in the series Z, W, T, Q, ?
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    Answer: A. N

    The letters go back 3 each time: Z(26), W(23), T(20), Q(17), so next is 14, which is N.

  7. Question 7 of 18

    What number comes next in the series 5, 7, 11, 17, 25, ?
    Show answer

    Answer: D. 35

    The differences are 2, 4, 6, 8, so the next difference is 10: 25 + 10 = 35.

  8. Question 8 of 18

    What comes next in the series A1, C3, E5, G7, ?
    Show answer

    Answer: A. I9

    Each letter skips one, and the number is the letter's position in the alphabet: I is the 9th letter, so I9.

  9. Question 9 of 18

    What number comes next in the series 2, 5, 11, 23, ?
    Show answer

    Answer: A. 47

    Each number is doubled and then 1 is added: 23 × 2 + 1 = 47.

  10. Question 10 of 18

    What number comes next in the series 2, 3, 5, 8, 13, ?
    Show answer

    Answer: D. 21

    Each number is the sum of the two before it: 5 + 8 = 13, so 8 + 13 = 21.

  11. Question 11 of 18

    What comes next in the series AZ, BY, CX, DW, ?
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    Answer: A. EV

    The first letter moves forward one place (A, B, C, D, E) and the second moves back one place (Z, Y, X, W, V).

  12. Question 12 of 18

    What number comes next in the series 10, 3, 12, 6, 14, 9, ?
    Show answer

    Answer: C. 16

    Two series alternate: 10, 12, 14 (add 2) and 3, 6, 9 (add 3). The next number belongs to the first series: 14 + 2 = 16.

  13. Question 13 of 18

    What letter comes next in the series B, D, G, K, ?
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    Answer: A. P

    The gaps grow: +2, +3, +4, so the next gap is +5. K is 11, and 11 + 5 = 16, which is P.

  14. Question 14 of 18

    What number comes next in the series 100, 50, 52, 26, 28, ?
    Show answer

    Answer: D. 14

    The steps alternate: divide by 2, then add 2. After 28 comes 28 ÷ 2 = 14.

  15. Question 15 of 18

    What number comes next in the series 1, 2, 6, 24, 120, ?
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    Answer: D. 720

    Multiply by 2, then 3, then 4, then 5. The next step is × 6: 120 × 6 = 720.

  16. Question 16 of 18

    One number in this series is wrong: 2, 6, 18, 52, 162. Which one?
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    Answer: A. 52

    Each number should be 3 times the one before: 2, 6, 18, 54, 162. So 52 should be 54.

  17. Question 17 of 18

    What letter comes next in the series D, F, I, M, R, ?
    Show answer

    Answer: A. X

    The gaps are +2, +3, +4, +5, so the next gap is +6. R is 18, and 18 + 6 = 24, which is X.

  18. Question 18 of 18

    What number comes next in the series 3, 4, 8, 17, 33, ?
    Show answer

    Answer: C. 58

    The differences are 1, 4, 9, 16 (square numbers). The next difference is 25: 33 + 25 = 58.

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