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GMAT Exam pack 2 - DS - Geometry

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by lucas211 » Thu Jun 23, 2016 3:55 am
Hello BTG

Would appreciate a little help on the question below, and especially why C is not the right answer.
My approach here is, that combined we know that the "3-4-5"-triangle is a right triangle (or is it ?).
Since we know that the diameter is AB (and therefore the longest line possible inscribed in the circle), we can determine the diameter to 5, and through this calculate the circumference.

Thanks in advance
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Source: — Data Sufficiency |
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by DavidG@VeritasPrep » Thu Jun 23, 2016 5:18 am
lucas211 wrote:Hello BTG

Would appreciate a little help on the question below, and especially why C is not the right answer.
My approach here is, that combined we know that the "3-4-5"-triangle is a right triangle (or is it ?).
Since we know that the diameter is AB (and therefore the longest line possible inscribed in the circle), we can determine the diameter to 5, and through this calculate the circumference.

Thanks in advance
The ratio of the sides is 3:4:5, not the actual measurements. In other words, the actual measurements could be 3, 4, and 5 or they could be 6, 8, and 10, or 9, 12, 15, etc.
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by ceilidh.erickson » Thu Jun 23, 2016 6:29 am
lucas211 wrote:Hello BTG

Would appreciate a little help on the question below, and especially why C is not the right answer.
My approach here is, that combined we know that the "3-4-5"-triangle is a right triangle (or is it ?).
Since we know that the diameter is AB (and therefore the longest line possible inscribed in the circle), we can determine the diameter to 5, and through this calculate the circumference.

Thanks in advance
David is absolutely right about the ratio v. length.

One thing I want to add: If statement 2 had told us that the lengths were 3, 4, and 5, we wouldn't actually have needed statement 1 as well. Any triangle that has side lengths in the ratio 3:4:5 must be a right triangle (just as any triangle with 3 equal sides must be equilateral). If we knew it was a right triangle, then we'd know that the hypotenuse must be the diameter of the circle.
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by Matt@VeritasPrep » Thu Jun 23, 2016 5:47 pm
If the ratio is 3:4:5, we could have 3:4:5, or 6:8:10, or 9:12:15, or ...

The devil is in the details!

As a general strategy tip, if a DS question seems to be an obvious C, run screaming from answer C!
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