Alphanumeric Series & Position Puzzles

🎯 Learning Objective

Split mixed letter-number series into two chains and count positions in arrangements without slipping.

💡 Concept

• Alphanumeric terms mix letters and numbers: A1, C3, E5 … — treat them as TWO separate chains
• Solve the letter chain and the number chain independently, then combine the answers
• The two chains can follow different rules: numbers doubling while letter gaps grow
• Position puzzles give a row like B 7 K 4 M 9 T 2 W 5 and ask for elements at counted spots
• k-th to the RIGHT of the m-th from the LEFT = position (m + k) from the left
• k-th to the LEFT of the m-th from the RIGHT = position (m + k) from the right

🧮 Key Formulas

k-th right of m-th from left = (m + k)-th from left

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k-th left of m-th from right = (m + k)-th from right

✏️ Easy Example

Q. Find the next term: A1, C3, E5, G7, ?

1. Letters: A, C, E, G → next is I
2. Numbers: 1, 3, 5, 7 → next is 9
3. Combine: I9

Answer: I9

🇮🇳 Real-Life Example

Your train berth S5-32 mixes a letter chain (coach) and a number chain (berth). You already read alphanumeric series on every reservation chart.

📝 Exam-Level Example

Q. Find the next term: 2A, 4C, 8F, 16J, ?

1. Numbers: 2, 4, 8, 16 — doubling → 32
2. Letters: A(1), C(3), F(6), J(10) — gaps +2, +3, +4
3. Next gap +5 → 10 + 5 = 15 = O

Answer: 32O

📝 Exam-Level Example

Q. In the arrangement B 7 K 4 M 9 T 2 W 5, which element is 4th to the right of the 2nd element from the left?

1. 2nd from the left = 7 (position 2)
2. 4th to its right = position 2 + 4 = 6
3. Position 6 = 9

Answer: 9

🪄 Memory Trick

Split first, solve later — letters on one line, numbers on another. For positions, convert every phrase into a single count: (m + k).

⚠️ Common Mistakes

• ❌ Solving letters and numbers as one mixed pattern
• ❌ Confusing 'to the left of' with 'from the left'
• ❌ Counting the starting element itself while moving right or left

🏆 Exam Tips

• ✅ Rewrite the two chains separately on rough paper — 10 seconds that save a mark
• ✅ Number the positions 1, 2, 3 … above the arrangement before answering

📌 Summary

• Alphanumeric = two independent chains
• Solve letters and numbers separately, then combine
• k-th right of m-th from left = (m + k)-th from left
• Write position numbers above the row