Alphanumeric Series

Alphanumeric series gives you a single mixed row of capital letters, digits and symbols and then asks counting questions about it — how many numbers are immediately followed by a letter, how many symbols sit between two markers, and so on. In SBI Clerk this is one of the fastest scoring blocks, worth three to five marks, because it needs no theory at all: just careful, one-directional scanning of a row you can see. The whole skill is reading the condition correctly and marking as you move. There is nothing to memorise and nothing to calculate, which makes these questions the ideal place to open your Reasoning attempt and build a rhythm before the heavier puzzle and seating sets arrive.

The One Rule: Read the Direction of the Condition

Every alphanumeric question hangs on a phrase like 'immediately followed by' or 'immediately preceded by', and the two are opposite directions. 'A number followed by a letter' means the number comes first and a letter sits to its right; 'preceded by' means the letter is on the left. Underline the condition word before you scan, because reversing it is the single biggest cause of a wrong count in this topic. The word 'immediately' matters just as much: it means the two elements must be adjacent with nothing between them, so a matching pair separated by even one symbol does not count.

Shortcut: Scan Once With a Finger, Mark Hits

Do not re-read the row for every option. Place your pen under the first element and slide right once, checking each element against the condition and putting a tiny tick above every hit. One pass gives you the full count. For a 'both sides' condition — a digit flanked by two symbols — check the left and right neighbour together at each digit, still in a single sweep across the row.

Followed by = pattern reads LEFT to RIGHT (X then Y). Preceded by = Y then X.

Handling 'Both Neighbours' Conditions

The harder variant asks for an element with a specific left neighbour and a specific right neighbour at once, such as a letter with a number before it and a symbol after it. Treat each candidate as the middle of a three-element window and test both edges; if either fails, reject it. Never count an element sitting at the very start or very end of the row for a both-sides condition, because it is missing one neighbour. A related variant inserts a fresh element after every group of three, or reverses the whole row before asking, so always act on the row exactly as the question finally presents it, not the original you first read, and redraw the modified row on your sheet before you begin counting.

Solved Examples

Row: 5 K @ 3 P 7 % Q 2 R # 8 M. Q1: How many numbers are immediately followed by a letter? Scan: 3 then P (hit), 2 then R (hit) — the others are followed by symbols. Answer 2. Q2: How many symbols are immediately preceded by a number? @ after 5 no, % after 7 yes, # after 2 yes — answer 2.

✗ Counting a letter followed by a number when asked for 'number followed by letter'  |  ✓ Fixing the order first: number on the left, letter on its right