How to solve letter series

Number the alphabet first

Before you start, write the alphabet with each letter's position: A = 1, B = 2, C = 3 and so on. It takes a few seconds and prevents most counting errors. For series that run backwards, number the letters from the end as well.

Check whether the test specifies the alphabet. The English alphabet has 26 letters, but others differ: the Spanish alphabet, for example, adds Ñ after N, which shifts every later letter by one position.

Solve the numbers, not the letters

Use the same three steps for every letter series:

1. Convert every letter to its position and write the numbers under the series.
2. Look for a pattern in the numbers, using the checks you would use for a number series: constant differences, growing differences or two series interleaved.
3. Convert the result back into a letter using the same alphabet. If it goes past the last letter, check whether the test continues from the beginning.

Example: growing steps

Convert the letters into positions before looking for the rule.

Example: two series in one

When neighboring letters seem unrelated, separate the odd and even positions.

Example: why the alphabet matters

The same rule can give different letters depending on the alphabet. Count carefully after N.

Mistakes to watch for

Counting from A every time instead of using a written list, mixing the positions of two alphabets, missing a series that runs backwards and checking only the last two letters. Once you have an answer, check it against every step in the series.