You saw “series completion” on a practice test or in a prep site’s question list, and you want to know what it is before your assessment link expires. Here is the direct answer: series completion is any question that shows part of a sequence and asks what comes next, and on the CCAT it turns up in three costumes, as numbers, as letters, and as shapes or symbols. They look nothing alike on screen, but one procedure cracks all three in about 10 seconds each: name what is changing, test the cheapest rule that could explain it, then verify that rule on one more step before you answer.
One quick disambiguation before you start. This is the Criteria Cognitive Aptitude Test used in workplace hiring, not the Canadian Cognitive Abilities Test given to schoolchildren that shares the same initials. Plenty of the “CCAT series” material online is quietly about the children’s test.
Quick takeaways
- Series completion is not one CCAT question type. It shows up as number and letter series in the Math and Logic area, and as shape or symbol series in Spatial Reasoning.
- Sentence completion is a verbal question, not a series question, and matrix completion is the 3x3 grid variant. Do not buy practice material for the wrong one.
- “Series completion” is prep-site shorthand, not an official Criteria Corp label, which is why different sites define it differently.
- The method is identical for all three flavors: name the dimension that changes, test the cheapest rule first, verify that rule on one more step before answering.
- The CCAT is 50 questions in 15 minutes, about 18 seconds each, so a series item you cannot crack in roughly 10 seconds is a guess-and-move situation.
- Letter series become easy the moment you convert letters to alphabet positions, because then they are just number series.
- Shape series only ever change six things: rotation, reflection, shading, count, size, or position.
What “series completion” actually means on the CCAT
Series completion is a family of question formats, not an officially named section. Criteria Corp, which publishes the CCAT, describes the test as 50 questions in 15 minutes across Verbal, Math and Logic, and Spatial Reasoning questions, with no calculator allowed. It does not publish a per-type question count, so any site quoting you an exact number of series items is estimating. What you can rely on is where each flavor lives.
| Term you might see | What it actually is | Where it sits on the CCAT |
|---|---|---|
| Number series | A run of numbers with the next value missing | Math and Logic |
| Letter series | Single letters or letter pairs following an alphabet rule | Math and Logic |
| Shape or symbol series, “next in series” | Figures that change step by step across a row | Spatial Reasoning |
| Matrix completion | A 3x3 grid of figures with one cell blank | Spatial Reasoning |
| Sentence completion | A sentence with a missing word | Verbal, not a series question at all |
That last row trips people up constantly. If you searched for CCAT series completion and landed on a page about context clues and grammar, you were reading about sentence completion, a different skill entirely. The other mix-up is bigger: the school-level Canadian Cognitive Abilities Test also has a number series section, so a share of search results, and a share of AI-written answers, describe a test built for eleven-year-olds. If a page mentions grade levels, stanines or a child’s score report, close it.
The 10-second rule: a three-step procedure
Every series question, in any format, is solved by the same three moves in the same order.
- Name the dimension that changes. Ask what is different from one term to the next. With numbers it is size and direction, with letters it is alphabet position, with shapes it is one of six visual properties. Give this about two seconds.
- Test the cheapest rule first. Cheap means fewest mental operations: add or subtract before multiply or divide, one rule before two interleaved rules, single change before combined change. Most CCAT series run on a cheap rule.
- Verify on one more step. A rule that explains term one to term two is a guess. A rule that also explains term two to term three is an answer. People skip this step, and it is where most wrong answers come from.
Why 10 seconds? Fifty questions in fifteen minutes is roughly 18 seconds each, and series items are meant to be your fast points, the ones that bank time for word problems and longer verbal items later. Criteria Corp notes that fewer than 1 percent of candidates answer all 50 questions, so the test is built to run you out of clock. Ten seconds is a budget, not a target.
Numbers: the checking order that finds the rule fastest
For a number series, run these checks in a fixed order and stop at the first one that holds twice.
- Constant difference. Subtract each term from the next; if the gaps match, you are done.
- Constant ratio. Divide each term by the previous one. Doubling, tripling and halving are common.
- Pattern in the differences. Write the gaps out. If the gaps form a simple run like 2, 4, 6, 8, that is your rule.
- Two interleaved series. Read the odd positions only, then the even positions only. Two simple rules hiding in one row look impossible until you split them.
Worked example: 4, 9, 19, 39, ? The differences are 5, 10, 20, not constant, and the ratios are not clean, so this is not a pure geometric run. But the differences are doubling, which points at an operate-then-add rule. Test the cheapest candidate, multiply by 2 and add 1: 4 times 2 plus 1 is 9. Verify on the next step: 9 times 2 plus 1 is 19. The rule holds twice, so the answer is 39 times 2 plus 1, which is 79.
For the full pattern catalogue, our five CCAT number series patterns piece is the companion to this one, and the older number sequences deep dive covers mixed operations.
Letters: convert to positions, then it is a number series
A letter series is a number series in disguise. Write A equals 1, B equals 2, through to Z equals 26, and the alphabet gaps become arithmetic you already know how to check.
Worked example: C, F, J, O, ? The positions are 3, 6, 10, 15. The differences are 3, 4, 5, so the next gap is 6. Position 15 plus 6 is 21, which is U.
Two things to watch. Series often run in pairs, like AZ, BY, CX, where the first letter walks forward while the second walks backward, so split the pair and treat each position as its own series. And some series wrap past Z back to A, so if your arithmetic gives position 28, subtract 26 and take position 2, which is B. Neither is hard, but both cost time if you meet them first on test day.
Shapes and symbols: six things that can change
Shape series feel harder because there is no arithmetic to fall back on, but the search space is smaller than it looks. A figure in a CCAT-style series is changing one of six properties, and your whole job in step one is to name which.
Worked example, described the way you would see it on screen. Box one: a triangle pointing up with a black dot in the top-left corner. Box two: the same triangle rotated 90 degrees clockwise, dot now top-right. Box three: rotated another 90 degrees, dot bottom-right.
Two properties are moving, so handle them separately. The triangle turns 90 degrees clockwise per step, putting the fourth figure 270 degrees from the start. The dot moves one corner clockwise per step, so it lands bottom-left. Both rules hold across both jumps, so scan the options for the single figure that satisfies both. When two properties change at once, at least one distractor will get exactly one of them right. The same scan works on matrix questions, read across the rows first and then down the columns, and our CCAT abstract reasoning guide covers those variants.
