Number & Alphabet Series • Topic 4 of 4

Missing & Wrong Term

To find a missing term, establish the rule from the surrounding terms and fill the gap. To find the wrong term, compute what each term should be from the rule and flag the one that doesn't fit. Re-derive the rule from at least three clean terms first.

Build the rule from clean terms first

For a missing term, work out the rule from the terms you can see, then fill the blank. For a wrong term, predict what each term should be and flag the mismatch.

Example (wrong term): 2, 6, 12, 20, 30, 41. The rule is n(n+1): 2, 6, 12, 20, 30, 42. So 41 is wrong — it should be 42.

Don't trust two terms. Establish the pattern from at least three consecutive clean terms before declaring a term wrong; a single early outlier can fool you into the wrong rule.

✅ Solved examples

1. Missing: 4, 9, 16, ?, 36.
Squares 2,3,4,5,6 → 5^2 = 25.
2. Wrong term: 2, 6, 12, 20, 30, 41.
Should be n(n+1): 2,6,12,20,30,42. 41 is wrong (→42).
3. Missing: 3, 6, 12, ?, 48.
Ratio ×2 → 12 × 2 = 24.
4. Wrong term: 5, 11, 17, 23, 30.
+6 each → 5,11,17,23,29. 30 is wrong (→29).

✏️ Practice — try these, take hints as needed

1. Missing: 1, 4, 9, 16, ?
Squares.
5^2.
—
25
2. Wrong: 3, 5, 7, 9, 10, 13.
Odd numbers / +2.
10 breaks it.
—
10
3. Missing: 2, 4, 8, ?, 32.
×2.
8×2.
—
16
4. Wrong: 6, 12, 18, 24, 32.
+6.
24+6=30.
—
32
5. Missing: 7, 14, 28, ?, 112.
×2.
28×2.
—
56

📝 Topic test — 8 questions

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