Alphanumeric series for LIC AAO

An alphanumeric series question gives you a line of 15 to 25 elements (letters, digits and symbols) and asks four or five questions about it. Nothing in it needs insight. It needs careful counting, and that is exactly why candidates lose marks here: they count in their heads, slip by one, and the wrong answer is sitting among the options.

Set up before you read a single question

1. Write position numbers 1, 2, 3… under the series on your rough sheet. This takes about 20 seconds and removes most errors.
2. Mark vowels (A, E, I, O, U) with a dot if any question mentions them. Everything else that is a letter is a consonant.
3. Note the total number of elements, N. You will need it for every "from the right" question.

The position arithmetic

"To the left" always means towards the start of the series, and "to the right" towards its end, whichever end you counted from. The formula N − k + 1 is the same one you use in order and ranking, for the same reason.

Reading the relation phrases

• "X immediately followed by Y": Y is the next element to the right of X.
• "X immediately preceded by Y": Y is the element just to the left of X.
• "Preceded by a number and followed by a symbol": look at both neighbours of the middle element.
• "Removed" or "dropped": rewrite the shorter series before counting. Do not count around gaps in your head.
• "If the series is reversed": the k-th from the left in the reversed series is the k-th from the right in the original. You rarely need to rewrite it.

A fully worked set

Series: 7 M @ 3 B K # 9 E 4 $ R 2 T % 6 H

N = 17.

Q1. How many numbers are immediately followed by a letter?

• 7M, 3B, 9E, 2T, 6H. Five. The 4 is followed by $, so it does not count.

Q2. How many symbols are immediately preceded by a letter?

• M@, K#, T%. Three. The $ is preceded by 4.

Q3. Which element is sixth from the right end?

• 17 − 6 + 1 = 12th from the left. R.
• Check by counting from the right end: H, 6, %, T, 2, R.

Q4. Which element is fifth to the left of the twelfth element from the left?

• 12 − 5 = 7. #.

Q5. If all symbols are removed, which element is eighth from the left?

• New series: 7 M 3 B K 9 E 4 R 2 T 6 H. Eighth is 4.

Q6. How many letters are immediately preceded by a number and immediately followed by a symbol?

• Check each letter's two neighbours: 7 M @ fits, and 2 T % fits. B, K, E, R and H do not. Two.

Q7. Which element is exactly midway between 3 and T?

• 3 is at 4 and T is at 14. (4 + 14) ÷ 2 = 9. E.

Q8. M @ 3 is related to K # 9 in a certain way. In the same way, $ R 2 is related to what?

• M, @, 3 are at 2, 3, 4. K, #, 9 are at 6, 7, 8. Each element moves four places right.
• $, R, 2 are at 11, 12, 13, so the answer is at 15, 16, 17: % 6 H.

Q9. If the series is reversed, which element is fourth to the right of the tenth element from the left?

• The 10th from the left in the reversed series is the 10th from the right in the original: 17 − 10 + 1 = 8, which is 9.
• "To the right" in the reversed series is "to the left" in the original: 8 − 4 = 4. 3.
• Check by writing the reversed series: H 6 % T 2 R $ 4 E 9 # K B 3 @ M 7. The 10th is 9 and the 14th is 3.

English alphabet questions

The same arithmetic works on the alphabet, where N = 26.

• Learn the positions EJOTY: E = 5, J = 10, O = 15, T = 20, Y = 25.
• Position from the right = 27 − position from the left. M is 13th from the left and 14th from the right.
• Opposite pairs add up to 27: A–Z, B–Y, C–X, M–N.

Example. If the second half of the alphabet (N to Z) is written in reverse order, which letter is fifth to the right of the tenth letter from the left?

• The first half A to M is unchanged, so the tenth letter is J.
• Fifth to its right is position 15. Positions 14 onwards now read Z, Y, X…, so position 15 is Y.

Practice set

Series: D 5 # K 8 A R @ 2 U 9 $ P 3 L % 7 E

1. How many vowels are there in the series?
2. How many numbers are immediately preceded by a consonant?
3. Which element is seventh from the right end?
4. Which element is fifth to the right of the sixth element from the left?
5. If all numbers are removed, which element is ninth from the left?
6. How many symbols are immediately followed by a number?
7. Which letter of the English alphabet is sixth to the left of the twentieth letter from the left?
8. If the alphabet is written in reverse order, which letter is eighth from the left?

Answers

1. Three. A, U and E.
2. Three. D5, K8 and P3. The 9 is preceded by U, a vowel.
3. $. N = 18, so 18 − 7 + 1 = 12th from the left.
4. 9. The sixth element is A; 6 + 5 = 11.
5. P. The series becomes D # K A R @ U $ P L % E.
6. Two. @2 and %7.
7. N. T is 20th; 20 − 6 = 14, which is N.
8. S. Eighth from the left in reverse is eighth from the right: 27 − 8 = 19, which is S.

A quick routine

• Number the positions and write N before answering anything.
• For every "from the right", write N − k + 1 on paper.
• For "removed" questions, rewrite the series. It is faster than recounting twice.
• For conditions with two neighbours, check the left neighbour, then the right, then the element itself.
• Recount any answer that needed more than ten steps of counting.

What to do next

• Time yourself on ten alphanumeric questions. Aim for under 30 seconds each with no errors.
• Revise the position formula alongside order and ranking.
• Letter shifts and reverse positions also drive coding–decoding. Practise both in the same week.