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What is the measure of angle BAD?

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What is the measure of angle BAD?

by melguy » Sun Aug 18, 2013 10:05 pm
Hello

It is an easy Q but I am a bit confused with the bisect concept here. Line 2 can bisect BAC at a different angle too. Or does bisect by definition means equally divide?

Thanks
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Source: — Data Sufficiency |

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by [email protected] » Sun Aug 18, 2013 10:21 pm
Hi melguy,

The word "bisect" means "to cut into 2 equal pieces"; for example, bisecting a 20 degree angle would yield two 10 degree angles. Knowing that definition will make this DS question fairly straightforward.

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by ganeshrkamath » Mon Aug 19, 2013 12:50 am
melguy wrote:Hello

It is an easy Q but I am a bit confused with the bisect concept here. Line 2 can bisect BAC at a different angle too. Or does bisect by definition means equally divide?

Thanks
melguy,

Bisect, by definition, means to divide into 2 equal parts.
So bisect an angle means divide that angle by 2.
Bisect a line means divide that line into 2 equal halves.

Similarly, trisect means to divide into 3 equal parts.

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by Brent@GMATPrepNow » Mon Aug 19, 2013 6:08 am
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If anyone wishes to attempt the original question, here's one solution:

Target question: What is the measure of angle BAD?

Statement 1: AD bisects angle BAC
Since we don't know the measure of angle BAC, there's no way to determine the measure of angle BAD
Since we cannot answer the target question with certainty, statement 1 is NOT SUFFICIENT

Statement 2: BAC is an isosceles right triangle
This statement contains no information about D, so there's no way to determine the measure of angle BAD
Since we cannot answer the target question with certainty, statement 2 is NOT SUFFICIENT

Statements 1 and 2 combined
If BAC is an isosceles right triangle, then angle BAC = 45 degrees
If AD bisects angle BAC, then angle BAD = 22.5 degrees
Since we can answer the target question with certainty, the combined statements are SUFFICIENT

Answer = C

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