In the letter pair series BD, EG, HJ, ?, which pair of letters should come next to continue the pattern?

Introduction / Context:
This question gives a short alphabet series made of letter pairs: BD, EG, HJ, ?. You are asked to identify which pair of letters should come next. Such problems test basic understanding of alphabetical positions and constant differences, so they are common in aptitude and reasoning exams.

Given Data / Assumptions:

• Series terms: BD, EG, HJ, ?
• Each term is a pair of letters.
• We use alphabet positions A 1, B 2, C 3, ..., Z 26.
• The same pattern should apply to both letters of each pair.

Concept / Approach:
The main idea is to separate the first letters of each pair and the second letters of each pair, then treat them as two numeric sequences. If both sequences follow a constant step, we can extend them to find the missing pair. This column wise approach is very powerful for two letter series.

Step-by-Step Solution:
Step 1: Take first letters: B, E, H, ?. Step 2: Convert to numbers: B 2, E 5, H 8. Step 3: Differences are 5 minus 2 equals 3 and 8 minus 5 equals 3. So the first letters increase by 3 each time. Step 4: Add 3 again to get the next first letter: 8 plus 3 equals 11, which is K. Step 5: Now take second letters: D, G, J, ?. Step 6: Convert to numbers: D 4, G 7, J 10. Step 7: Differences are 7 minus 4 equals 3 and 10 minus 7 equals 3. So the second letters also increase by 3. Step 8: Add 3 again: 10 plus 3 equals 13, which is M. Step 9: Therefore the missing pair is KM.

Verification / Alternative check:
Write all pairs with positions: BD 2,4; EG 5,7; HJ 8,10; KM 11,13. In both columns the numbers form simple arithmetic progressions with common difference 3. There is no break in the pattern, so KM fits naturally.

Why Other Options Are Wrong:
LN has positions 12,14, which would require the first column to jump by 4 from 8 to 12. LM and KN disturb at least one of the two arithmetic progressions. Only KM keeps the same difference of 3 for both letters simultaneously.

Common Pitfalls:
Many learners look only at the visual gap between letters without converting to numbers, which makes it easy to miscount. Others check only the first letter pattern and then guess a second letter. The safe method is always to check the difference for both letters separately and ensure consistency.

Final Answer:
The pair of letters that continues the series is KM.