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Calculator for a DS solution?

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dandarth1
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Calculator for a DS solution? [#permalink] New post   04 Sep 2012, 21:21
Hi! I'll illustrate my confusion by using a DS question:

Are all angles of triangle ABC smaller than 90 degrees?

(1) 2AB=3BC=4AC

(2) AC2+AB2>BC2

So the first given is sufficient, because if we have the ratio of all of the sides of a triangle, then we can find out all of the angles. However, we would need a calculator to that with a bit of trig right? This question is from the gmatclub tests, and it says 1) is sufficient. I just want to make sure that these DS questions are asking merely if the solution is attainable from the given, with or without a calculator, OR if it is specifically attainable without a calculator? I hope that makes sense. Thanks in advance!
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KapTeacherEli
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Re: Calculator for a DS solution? [#permalink] New post   04 Sep 2012, 22:58
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dandarth1 wrote:
Hi! I'll illustrate my confusion by using a DS question:

Are all angles of triangle ABC smaller than 90 degrees?

(1) 2AB=3BC=4AC

(2) AC2+AB2>BC2

So the first given is sufficient, because if we have the ratio of all of the sides of a triangle, then we can find out all of the angles. However, we would need a calculator to that with a bit of trig right? This question is from the gmatclub tests, and it says 1) is sufficient. I just want to make sure that these DS questions are asking merely if the solution is attainable from the given, with or without a calculator, OR if it is specifically attainable without a calculator? I hope that makes sense. Thanks in advance!
you've got it. DS questions care only that there is a single solution. Whether that solution is attainable through simple arithmetic or through complex trigonometry is irrelevant. In fact, a few concepts, such as standard deviation, will never be calculable by hand when they appear!
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dandarth1
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Re: Calculator for a DS solution? [#permalink] New post   04 Sep 2012, 23:00
KapTeacherEli wrote:
dandarth1 wrote:
Hi! I'll illustrate my confusion by using a DS question:

Are all angles of triangle ABC smaller than 90 degrees?

(1) 2AB=3BC=4AC

(2) AC2+AB2>BC2

So the first given is sufficient, because if we have the ratio of all of the sides of a triangle, then we can find out all of the angles. However, we would need a calculator to that with a bit of trig right? This question is from the gmatclub tests, and it says 1) is sufficient. I just want to make sure that these DS questions are asking merely if the solution is attainable from the given, with or without a calculator, OR if it is specifically attainable without a calculator? I hope that makes sense. Thanks in advance!
you've got it. DS questions care only that there is a single solution. Whether that solution is attainable through simple arithmetic or through complex trigonometry is irrelevant. In fact, a few concepts, such as standard deviation, will never be calculable by hand when they appear!


Thanks!! You are like an angel from the gmat heavens ;)
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Re: Calculator for a DS solution? [#permalink] New post   06 Feb 2013, 09:08
HI
I marked D as the answer for this one.
Because we know that for right angle triangle hypotenuse is AC (say C)
C^2 = a^2 + b^2
but when angle is greater than 90:
C^2>a^2 +b^2

So cant we say that if it is given C^2<a^2+b^2, angles in the triangle are less than 90 deg........
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Re: Calculator for a DS solution? [#permalink] New post   06 Feb 2013, 20:24
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Archit143 wrote:
HI
I marked D as the answer for this one.
Because we know that for right angle triangle hypotenuse is AC (say C)


How do you know which side is the hypotenuse? Can you say that BC must be the hypotenuse?

Say, think of the triangle 3-4-5. Perhaps AB = 5, BC = 4 and AC = 3
\(AC^2+AB^2>BC^2\) holds for these values. So ABC could be a right angle triangle and hence all angles will not be less than 90.

Say, if sides are AB = 4.5, BC = 4 and AC = 3
\(AC^2+AB^2>BC^2\) still holds but all angles in this case will be less than 90.

So statement 2 is not sufficient alone.
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Re: Calculator for a DS solution? [#permalink]
06 Feb 2013, 20:24

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