Explain number and letter series with their types and the method of solving, with examples.

1. 1 · Open in two lines. A series is a list of numbers or letters that follows one hidden rule. The task is to find the next, missing or wrong term.
2. 2 · Draw the method. [Diagram: Look at growth → Differences → Ratios → Squares and cubes → Alternate terms → Confirm on every term]
3. 3 · Number series types.
   • Constant difference: 7, 12, 17, 22 (+5).
   • Growing difference: 2, 5, 10, 17, 26 (+3, +5, +7, +9).
   • Ratio: 3, 6, 12, 24 (×2); mixed rule: 2, 5, 11, 23 (×2 + 1).
   • Squares and cubes: 1, 4, 9, 16 and 1, 8, 27, 64; alternate: 2, 10, 4, 20, 6, 30.
4. 4 · Letter series.
   • Change letters to positions (A = 1 … Z = 26); remember EJOTY = 5, 10, 15, 20, 25.
   • Skip pattern: B, E, H, K, N (+3).
   • Pairs: AC, FH, KM, PR, UW (+5 each).
5. 5 · Wrong-term series. Find the rule from most terms, then spot the one that breaks it: in 3, 7, 15, 31, 64, 127 the rule is ×2 + 1, so 64 should be 63.
6. 6 · A worked example. 6, 11, 21, 36, 56, ?: the differences are 5, 10, 15, 20, so the next term is 56 + 25 = 81.
7. 7 · Use in competitive exams. Bank papers set missing-number and wrong-number series; SSC and placement tests mix in letter and alphanumeric series.
8. 8 · Close in one line. Test differences, ratios, powers and alternate terms in that order, and confirm the rule on every term.

Scoring tip: Write the differences or the rule under the series in your answer; it shows the examiner your method.