Number sequence exercises (with answers)
Number sequences train the skill of finding the rule behind a series. Try each one before revealing the answer.
How to solve a sequence
A simple routine that works in most cases:
- Work out the difference between neighbouring terms. Is it constant? Growing?
- If it is not addition, try multiplication or division.
- Look for squares (1, 4, 9, 16…) or the sum of the two previous terms.
- Check the rule against every term, not only the first two.
Exercises
1. 3, 7, 15, 31, ?
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63 — Each term is the previous × 2 + 1: 31 × 2 + 1 = 63.
2. 2, 8, 18, 32, ?
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50 — They are 2 × 1², 2 × 2², 2 × 3², 2 × 4²; next is 2 × 5² = 50.
3. 5, 8, 13, 21, 34, ?
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55 — Each term is the sum of the two before: 21 + 34 = 55.
4. 80, 40, 20, 10, ?
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5 — Each term is half the previous one: 10 ÷ 2 = 5.
5. 4, 6, 10, 18, ?
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34 — The differences double (+2, +4, +8); next is +16: 18 + 16 = 34.
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This test is recreational and educational. It is not a clinical or psychological assessment and does not replace a professional evaluation.