Letter Codes & Number Sequences — 11+ VR Topic Guide

Part of the GrammarMock topic guides. Drill with the Sequences & Codes mini-test after reading.

Why these questions are free marks (once trained)

Letter codes and number sequences are the most mechanical questions on a GL Verbal Reasoning paper. Unlike vocabulary questions, they don't depend on what your child happens to have read — they depend on a small set of techniques that can be fully trained in two weeks. A child who has drilled these should expect to get close to 100% on them, banking marks that offset the less predictable vocabulary sections.

Letter codes

"If the code for CAT is DBU, what is the code for DOG?"

Every letter-code question hides a shift rule: each letter has been moved a fixed number of places along the alphabet.

The method (teach it as three steps):

1. Write the alphabet out at the top of your working space the moment the section starts: ABCDEFGHIJKLMNOPQRSTUVWXYZ GL papers print it for you in the instructions — use it, don't do alphabet hopping in your head.

2. Find the shift from the solved pair. C→D is +1. A→B is +1. T→U is +1. Rule: shift forward 1. Always check ALL letters, not just the first — occasionally papers use alternating shifts (+1, +2, +1, +2), and checking every letter catches this.

3. Apply it to the new word: D→E, O→P, G→H. Answer: EPH.

Watch for: shifts that wrap around the end of the alphabet (Y + 3 = B), and backward shifts (HAND → GZMC is −1; the A wrapping back to Z is the giveaway).

Counting trick: for wraps, teach "the alphabet is a circle". Y+3: Y→Z is 1, Z→A is 2, A→B is 3.

Number sequences

"What comes next: 3, 4, 7, 11, 18, ?"

There are only five rule families GL uses. Teach your child to test them in this order:

1. Constant difference — same number added each time (5, 9, 13, 17 → +4)
2. Changing difference — differences grow or shrink by a pattern (2, 6, 12, 20 → differences 4, 6, 8, so next is +10)
3. Multiply/divide — each term × or ÷ a constant (3, 6, 12, 24 → ×2; 81, 27, 9 → ÷3)
4. Two-step rule — multiply then add (2, 5, 11, 23 → ×2 then +1)
5. Add the previous two — Fibonacci-style (3, 4, 7, 11, 18 → 11+18 = 29)

The working habit that gets the marks: write the differences between terms in the gaps above the sequence. Nine times out of ten, the differences reveal the rule instantly. If the differences look random, try dividing consecutive terms instead (rule 3 or 4), and if the third term equals the first two added, it's rule 5.

Special sequences worth memorising (they appear disguised as "spot the rule" but are really recognition):

• Squares: 1, 4, 9, 16, 25, 36, 49, 64, 81, 100
• Cubes: 1, 8, 27, 64, 125
• Triangular numbers: 1, 3, 6, 10, 15, 21, 28
• Powers of 2: 2, 4, 8, 16, 32, 64, 128

Letter arithmetic

"If A = 2, B = 4, C = 6, D = 8, E = 10, what letter is E − B + A?"

Pure substitution: 10 − 4 + 2 = 8, and 8 is the value of D. The only trap is rushing the arithmetic — teach left-to-right working with the substituted numbers written down, never done in the head.

Timing strategy

These sections reward speed. Target: 30 seconds per letter code, 40 seconds per sequence. If a sequence hasn't yielded to the difference test and the divide test within 45 seconds, guess (no negative marking on GL papers) and move on — one stubborn sequence isn't worth three vocabulary questions.