A code changes letters or numbers using a rule. A sequence puts them in an order with a pattern. Your job is to find a rule that fits every part of the example, then use it carefully.

Start with alphabet positions

A = 1, B = 2, C = 3, and so on to Z = 26. When practising, write the alphabet in a line and put the numbers underneath. In a test, follow its rules about rough work and any supplied alphabet.

Code type 1: move each letter

If CAT becomes DBU, every letter moves one place forward: C → D, A → B and T → U. Using that rule, DOG becomes EPH. Check all three letters before deciding that you have found the rule.

Some questions move backwards or use different moves in different positions. Only wrap from Z to A if the question's instructions or examples establish that rule.

Code type 2: swap a letter for a number

Using alphabet positions, BAD becomes 2–1–4. CAB becomes 3–1–2. Keep the numbers separate unless the instructions tell you to add or join them. The same letters could have a different code in another question.

Sequence type 1: equal jumps

In C, F, I, L, each letter moves forward three places. The next letter is O. You can check this with positions: 3, 6, 9, 12, 15.

Sequence type 2: changing jumps

Look at 2, 5, 9, 14. The jumps are +3, +4 and +5. Continuing with +6 gives 20. Write the gaps above the numbers if you are allowed rough work.

Sequence type 3: two patterns mixed together

In A, Z, C, X, E, V, the odd positions go A, C, E: forward two. The even positions go Z, X, V: back two. The next term is G because it belongs to the first pattern.

Try these

  1. If MAP becomes NBQ by moving each letter forward one place, what does SUN become?
  2. Using A = 1 to Z = 26, write the code for FACE.
  3. What comes next: B, E, H, K, …?
  4. Continue the increasing jumps: 4, 6, 9, 13, …
  5. What comes next: B, Y, D, W, F, U, …?
Show answers

1. TVO. 2. 6–1–3–5. 3. N (+3 letters). 4. 18 (+2, +3, +4, then +5). 5. H (the odd positions move forward two letters).

Before choosing an answer

Check the direction, count moves rather than the starting letter, and test the rule against every example. More than one mathematical rule can fit a short sequence; use the instructions and answer choices to identify the intended simple pattern. Practise these types only if they appear in your target test's guidance.