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To what extend should you trust the images provided with a question?

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Senior Manager
Joined: 08 Dec 2015
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GMAT 1: 600 Q44 V27
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20 Jul 2017, 09:54
Hi everyone, just came across this question: https://gmatclub.com/forum/in-the-figur ... 85154.html

I think that the image provided is misleading since it clearly contradicts the information provdied IF YOU TRUST THE IMAGE.

So, in PS, can we trust the images 100% (I always heard we can) since all the information necessary to answer is provided?

In DS we can't trust the image, it's just a general idea (since the info to answer is not provided in the question stem)

I am correct here?

Cheers!
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Re: To what extend should you trust the images provided with a question?  [#permalink]

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20 Jul 2017, 18:01
In general, do not assume anything about the geometric figures. They are usually not drawn to scale. Use the information provided in the question to derive the required data.
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21 Jul 2017, 08:39
you can trust some images if the question tells u that the picture is giving accurate information but usually it isnt the case. in most of the questions the image isnt drawn to scale or sometimes mislead you.
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21 Jul 2017, 08:52
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The instructions at the beginning of the test claim that diagrams are to scale in PS questions, unless otherwise stated - that is, unless they've rewritten those instructions in the last few years (I haven't read them in a long time). There's only one real GMAT PS question I've ever seen where the diagram is clearly not to scale, and the test doesn't mention the fact, and that's the question you've linked to above. So in general, you can probably trust diagrams in PS, but there may be rare exceptions. The safest policy is to redraw any diagrams yourself, properly to scale.

There are basic things about diagrams you can always assume are true. Lines that look straight are straight, for example, and if points are arranged in a certain order along a line, you can assume they are truly in that order.

The situation in DS is entirely different though. In DS, the exact diagram you can draw often depends on how much of the information in the statements you're using. In many geometry questions, it's usually true, before you use the statements, that a geometry diagram in DS could be drawn in a number of different ways. For example, if you don't know one of the angles in a diagram, clearly you could draw that angle in a variety of ways. So there's no way they even could draw the diagrams 'to scale' in DS, because there are usually many different potential diagrams you could draw using only the information in the question stem.
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Senior Manager
Joined: 08 Dec 2015
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22 Jul 2017, 09:19
Thank you all for your replies!

so probably this question is an exception then

Cheers and thank you for your input!
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23 Jul 2017, 14:45
1
"How much can I trust the diagrams?" is a really interesting question. It almost seems intuitive at first, but the more you think about it, the more you realize that it's a complicated question. Here's the simplest answer I can give:

- "Scale" applies to things like sizes and angles. For instance, if two triangles aren't drawn to scale, you don't know which one is larger and which one is smaller. You don't know which side of each triangle is the longest/shortest. You don't know their angles, so you don't know whether they're acute, obtuse, or right (unless the problem tells you). You don't know whether the triangles are equilateral or isosceles (unless the problem tells you). You don't know whether they're similar to each other (unless the problem tells you).

- If a diagram in a PS problem says 'not drawn to scale', you can't assume anything about sizes or angles based on the diagram.

- If it doesn't say 'not drawn to scale', the GMAT's rules say that it is drawn to scale. Therefore, you can use visual estimation. However, the problem above is an example of the GMAT breaking its own rules. If I saw a problem like this on an official test, assuming that wording is still in the rules, I might complain to the GMAC. To be safe, I'd also redraw diagrams and double-check that the scale matches the information I'm given in the problem.

- There are also things that the concept of scale just doesn't apply to. For example, suppose that a triangle isn't drawn to scale. You don't know much about it. But you do know that it's a triangle, and not, for example, a rectangle. They can't draw something that looks like it has three sides and tell you it actually has four sides, just because it's 'not to scale'.

Similarly, if there were four dots on a diagram, they couldn't say that there were actually five dots, just because it's 'not to scale'. The diagram has to be accurate to how many things there are (dots, sides, lines, etc.)

If two lines are shown to intersect in a diagram, you know that they intersect, even if the diagram isn't drawn to scale.

If one shape is drawn inside of another shape (for example, a dot inside of a circle), you know that it's inside the circle and not outside of the circle, even if it's not drawn to scale. You don't know exactly where inside of the circle it is, but you know that it's in there.

This bullet point also applies to Data Sufficiency. If there's a triangle drawn in a DS problem, you know that it's not necessarily to scale. You might be able to redraw it in multiple ways. However, you do know that it's a triangle and not a circle!
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To what extend should you trust the images provided with a question?   [#permalink] 23 Jul 2017, 14:45
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