11 plus Letter Series questions

What a Letter Series question looks like

Letter Series is one of the sequence puzzles that 11 plus verbal reasoning papers use. It prints a short run of letters and asks what comes next, and the pattern is always built on the alphabet: each letter has moved a certain number of places forward or backwards from the one before it. In the Letter Series questions your child will meet in 11+ Daily, the run is five pairs of letters with the sixth missing, and five possible pairs are offered.

What catches children out is that the two letters in a pair have nothing to do with each other. The first letters make one sequence with its own rule, the second letters another, and the two rules are usually different. Here are three, worked through in full.

The question. AA BC DE GG KI (?) with the options PK, PJ, PL, OK and QK.

The method. Take the first letter of each pair on its own: A, B, D, G, K. From A to B is one place, B to D is two, D to G is three, G to K is four. The gap is growing by one each time, so the next gap is five, and five places on from K is P. Now the second letters: A, C, E, G, I. Every gap is two, so two places on from I is K.

The answer. PK.

Why a wrong option tempts. OK is the trap here. A child who works out the gaps as one, two, three, four and then carries the last gap on instead of growing it counts four places from K and lands on O. The second letter is right, which makes the whole answer feel right. When the gaps are growing, the next gap is always one bigger than the one you just measured.

The question. BD CF FH GJ JL (?) with the options JN, KN, LN, KM and KO.

The method. First letters: B, C, F, G, J. B to C is one place, C to F is three, F to G is one, G to J is three. The gap is not growing here, it is taking turns: one, three, one, three. The last gap was three, so this one is one, and one place on from J is K. Second letters: D, F, H, J, L. Every gap is two, so two places on from L is N.

The answer. KN.

Why a wrong option tempts. KM has the right first letter and the second letter one place out. D, F, H, J, L is every other letter, and a child who is reading rather than counting slides on to the very next letter and writes M. Saying that run out loud as “D, skip E, F, skip G, H” makes the missing letter audible.

The question. BC CA EX HT LO (?) with the options RI, PI, QJ, QI and QH.

The method. First letters: B, C, E, H, L. The gaps are one, two, three, four, growing by one, so the next gap is five and five places on from L is Q. Second letters: C, A, X, T, O. These are going backwards. C back two is A. A back three would take you off the front of the alphabet, so you carry on from the end and land on X. X back four is T, T back five is O. The gaps are growing by one going backwards, so the next is six, and O back six is I.

The answer. QI.

Why a wrong option tempts. QJ is what a child gets by taking the second letter back five instead of six, the same “the gap stopped growing” slip as in the first example. PI is that slip on the first letter. Both are half right, which is why checking the finished pair against both rules is worth the few seconds it costs.

How to answer it

1. Write the alphabet out along the top of your paper before you look at the sequence. Nearly every mistake in this question type is a counting mistake, and having A to Z in front of you removes most of them.
2. Split the sequence in two. Write the first letter of each pair in one line and the second letters underneath. From here you are solving two easy puzzles instead of one hard one.
3. Count the gaps in each line and write the numbers down. Count the jumps between letters, not the letters themselves: A to B is a gap of one, not two.
4. Decide which of the three rules each line follows. The gaps either stay the same size, grow by one each time, or alternate between two sizes. If a line seems to go backwards past A, keep counting from Z.
5. Carry each rule on one more step, put the two letters together, and check the finished pair fits both lines before choosing it.

Common mistakes

• Letting the growing gap stop growing. When the gaps run one, two, three, four, the next one is five. Repeating the last gap gives an answer one letter short, and there is nearly always an option waiting for exactly that.
• Counting letters instead of jumps. A child who counts “A, B, that is two” ends up one place out at every step, and the answer still looks like a sensible pattern, which is what makes it hard to spot.
• Trying to read each pair as one thing. AA, BC, DE looks like it ought to mean something. It does not. Splitting the two letters into separate lines is the whole method.
• Getting stuck at the ends of the alphabet. Sequences that pass Z or fall off before A are not broken. Counting forward past Z carries on at A, and counting back past A carries on at Z.
• Missing an alternating rule. One, three, one, three is a pattern, not a mistake in the question. If the gaps neither sit still nor grow neatly, check whether they are taking turns.

How to practise 11 plus Letter Series questions

This is one of the eleven plus question types that rewards accuracy far more than cleverness. The reasoning is straightforward once the sequence has been split in two, and almost every lost mark comes from a miscount, so useful practice is short and frequent. Ten done carefully, with the alphabet written out, teach more than fifty done in a rush. 11+ Daily has a Letter Series project among its verbal reasoning skills, with the alphabet on screen while your child works, questions original to 11+ Daily rather than taken from past papers, and a full explanation of both rules after every answer. The Today screen decides when the skill comes round again, so it sits alongside the other codes and sequences work rather than being drilled alone. You can see how it fits with the rest on the 11 plus verbal reasoning page, and there is more on session length in our guide to how much 11 plus practice a child needs each day.

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