What is the measure of angle BAD?

[melguy]

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

[[email protected]]

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.

GMAT assassins aren't born, they're made,
Rich

[ganeshrkamath]

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.

Cheers

[Brent@GMATPrepNow]

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

Cheers,
Brent