Figure series, mirrors, embedded shapes and paper folding.
About Classification
In a classification question three of the four figures share a property and one does not, and the reader has to find the one that differs. The property is always something that can be counted or measured - the number of sides, the size, the number of marks inside, or the way the figure is turned - which is what makes the question answerable in a definite way rather than by impression. This topic covers that, and the rest of the non-verbal section it belongs to.
What you need to understand
A classification question is the mirror image of a series question. In a series the reader works out the rule and continues it; here the rule is already satisfied by three figures and has to be recognised from them.
The property shared by the three is always measurable, and there are only a few kinds that are used: the number of sides or lines, the number of small marks, the size of the figure, the angle it is turned through, and whether it is filled or open.
Counting sides is the commonest of them, and it is the one to try first. A polygon with a corner cut off has one more side than the same shape without, however similar the two look.
Size means the distance of the corners from the centre, not the area. Two figures can look much the same size while one of them has its corners noticeably further out.
The turn is the angle through which the figure has been rotated, and it is measured by the direction of a particular corner from the centre. Half a step of the shape is enough to separate two figures that look alike.
A figure that is the same shape but turned differently is not the odd one out if the question asks about sides. Read the question to see which property is being asked about before comparing anything.
The safest method is to measure the same property in all four figures and write the four values down. Four numbers in a row make the odd one obvious, and they stop the eye from being persuaded by an outline.
Working by impression is what the question is designed to defeat. Three of the four figures will differ from each other in some unimportant way - a jitter here, a slightly different corner - and the eye will seize on that instead of on the property being asked about.
When two properties seem to separate the figures, the one named in the question decides it. The others are noise, and following them is how a candidate talks themselves out of the right answer.
A figure with no marks at all is a legitimate member of a group: zero is a number, and a set with nought, nought, nought and one mark has a clear odd one out.
The classification question is also the way into the rest of the section. Analogy, series, matrix and rule detection all turn on the same habits - counting what is there, measuring rather than looking, and holding one property at a time in mind.
In an analogy question, the relation between the first pair has to hold between the second. It is the same skill as classification with the figures arranged in pairs rather than in a group.
In an embedded figure question the answer is not a shape that looks similar but one whose every side is covered by lines already drawn. A shape can be nearly right and still not be there.
In a paper folding question the fold line decides everything, and the holes are mirrored about it. Counting the holes before deciding where they fall answers most of these questions.
In a figure matrix the rule runs along the rows and down the columns, so the missing cell can be found from either direction. Finding it twice, once from each direction, is the check that the rule has been read correctly.
How to work through these questions
Read the question first and note which property is named. Then compare nothing else: the property named is the one that decides.
Count the sides of all four figures before looking at anything else. It is the commonest property and the cheapest to check.
For size, compare how far the corners sit from the middle rather than how much space the figure takes up. A turned square occupies the same area as the same square upright.
For a turn, find the same corner in each figure and see which way it points. The corners are hard to tell apart in a regular polygon, so use the marks inside if there are any.
Write the four values down in a line. It takes a few seconds and it removes the temptation to decide from the picture.
If the question seems to have two answers, one of the properties has been read from the wrong figure. Re-measure that property in all four and the ambiguity usually disappears.
Mistakes that cost marks
Choosing the figure that looks most different rather than the one that differs on the property the question names.
Counting the sides of a shape by its outline rather than by its corners. A small notch adds a side that is easy to miss.
Judging size by area or by how much of the space the figure fills, rather than by the distance of the corners from the centre.
Treating a figure with no marks as though it had a mark, and so counting the group as three against one when it is two against two.
Comparing the figures with each other before reading the question, which is how the wrong property gets chosen.
Taking the turn of a regular polygon from whichever corner is noticed first, when two corners of a hexagon can look identical at a glance.
Forgetting that in a matrix question the rule has to hold both along the rows and down the columns, so a cell that satisfies one direction may break the other.
In an embedded figure question, accepting a shape whose sides nearly line up with the drawing. Nearly is not covered, and the answer is wrong.
Worked example
Four figures are shown. Three of them have the same number of sides and one does not. How should the odd one be found?
Read the question first, and note that the property named is the number of sides. Nothing else on the page matters, however different the figures look.
Count the corners of each figure in turn, from a fixed point such as the top of the figure, and write the four numbers down in a line.
The three that share a side count will produce the same number three times, and the figure that breaks the group produces a different one. That figure is the answer.
Check the count of the odd figure once more, since it is the one the answer depends on. A triangle that has been drawn with a flat top can look like a quadrilateral until the corners are counted.
Notice what the method avoids. Deciding by impression would have been quicker and would have gone wrong: the three figures that share a side count differ from each other in their size and in the marks inside them, and the eye is drawn to those differences first.
Answer: Read the question, measure the named property in all four figures, and take the one that differs
Practice questions with answers
A few Classification questions with the full solution shown, so you can see
how the method is applied before you attempt the timed set.
Question 1
Which of these four figures is a different size from the other three?
AThe third figure
BThe fourth figure
CThe first figure
DThe second figure
Answer: Option D — with explanation
Three of the four figures are alike in one measurable way and the fourth is not, and the property the question names is the size.
Work through the figures one at a time and measure that property in each of them, rather than reading the shapes as pictures. Counting the sides of a regular polygon, or the marks inside it, or comparing how far the corners sit from the middle, gives a definite answer for each figure, and the one that does not match the other three is the answer.
Here the second figure is the one that differs; the other three agree on the size. The same method works whatever the property is - measure it in all four figures and look for the single one that breaks the pattern.
Common mistakes
- The third figure agrees with the other three: The third figure
- The fourth figure agrees with the other three: The fourth figure
- The first figure agrees with the other three: The first figure
Question 2
Which of these four figures is turned differently from the other three?
AThe second figure
BThe fourth figure
CThe first figure
DThe third figure
Answer: Option B — with explanation
Three of the four figures are alike in one measurable way and the fourth is not, and the property the question names is the way it is turned.
Work through the figures one at a time and measure that property in each of them, rather than reading the shapes as pictures. Counting the sides of a regular polygon, or the marks inside it, or comparing how far the corners sit from the middle, gives a definite answer for each figure, and the one that does not match the other three is the answer.
Here the fourth figure is the one that differs; the other three agree on the way it is turned. The same method works whatever the property is - measure it in all four figures and look for the single one that breaks the pattern.
Common mistakes
- The third figure agrees with the other three: The third figure
- The first figure agrees with the other three: The first figure
- The second figure agrees with the other three: The second figure
Question 3
Three of these four figures are the same size. Which one is not?
AThe fourth figure
BThe second figure
CThe first figure
DThe third figure
Answer: Option C — with explanation
Three of the four figures are alike in one measurable way and the fourth is not, and the property the question names is the size.
Work through the figures one at a time and measure that property in each of them, rather than reading the shapes as pictures. Counting the sides of a regular polygon, or the marks inside it, or comparing how far the corners sit from the middle, gives a definite answer for each figure, and the one that does not match the other three is the answer.
Here the first figure is the one that differs; the other three agree on the size. The same method works whatever the property is - measure it in all four figures and look for the single one that breaks the pattern.
Common mistakes
- The fourth figure agrees with the other three: The fourth figure
- The third figure agrees with the other three: The third figure
- The second figure agrees with the other three: The second figure
Question 4
Which of these four figures is turned differently from the other three?
AThe first figure
BThe fourth figure
CThe third figure
DThe second figure
Answer: Option B — with explanation
Three of the four figures are alike in one measurable way and the fourth is not, and the property the question names is the way it is turned.
Work through the figures one at a time and measure that property in each of them, rather than reading the shapes as pictures. Counting the sides of a regular polygon, or the marks inside it, or comparing how far the corners sit from the middle, gives a definite answer for each figure, and the one that does not match the other three is the answer.
Here the fourth figure is the one that differs; the other three agree on the way it is turned. The same method works whatever the property is - measure it in all four figures and look for the single one that breaks the pattern.
Common mistakes
- The third figure agrees with the other three: The third figure
- The first figure agrees with the other three: The first figure
- The second figure agrees with the other three: The second figure
Question 5
Three of these four figures have the same number of sides. Which one does not?
AThe third figure
BThe second figure
CThe first figure
DThe fourth figure
Answer: Option A — with explanation
Three of the four figures are alike in one measurable way and the fourth is not, and the property the question names is the number of sides.
Work through the figures one at a time and measure that property in each of them, rather than reading the shapes as pictures. Counting the sides of a regular polygon, or the marks inside it, or comparing how far the corners sit from the middle, gives a definite answer for each figure, and the one that does not match the other three is the answer.
Here the third figure is the one that differs; the other three agree on the number of sides. The same method works whatever the property is - measure it in all four figures and look for the single one that breaks the pattern.
Common mistakes
- The second figure agrees with the other three: The second figure
- The first figure agrees with the other three: The first figure
- The fourth figure agrees with the other three: The fourth figure
Frequently asked questions
How do I know which property the question is about?
The question says so: it names the number of sides, the size, the marks inside or the way the figure is turned. Read it before looking at the figures, because deciding from the pictures is how the wrong property gets chosen.
What if two figures seem to be odd?
Re-measure the named property in all four and write the values down. Two candidates for the odd one usually means the property has been read from the wrong figure, or that the question is about a different property than the one being compared.
Is a figure with no marks counted as having marks?
It has nought, which is a count like any other. A group of three figures with two marks each and one with none has an obvious odd one out, and the same group with one figure that has no marks and another that has four is not a classification question at all.
Does the turn of a figure matter if the question asks about sides?
No. A square turned through forty five degrees is still a square, and a question about sides counts four in both cases. Only the property named decides, which is why the question is read first.
Why are the figures not identical if they share a property?
Because they are drawn independently, so the marks inside them land in slightly different places. The property being asked about is held constant; everything else is allowed to vary, and noticing that is part of answering the question correctly.
What is the best way to practise this topic?
Work through sets of four figures and write down the side count of each, then the size, then the marks. The habit of measuring rather than looking is what carries over to the analogy, matrix and rule detection questions in this section.
Take the Classification test
Two timed papers on the same syllabus — sit the foundation paper first,
then the advanced one. Both use the real exam paper format with a full
step-by-step review of every question once you submit.
