Data Sufficiency

sydneyuni2014 wrote:Hello Brent

I was studying your video classes and came across the last geometry problem in the video. It asks what is the length of AB?
https://www.gmatprepnow.com/module/gmat ... video/1103

I am a bit confused. As per my understanding if we are unable to figure out a definitive value of a problem then the result should be E. Also, I would highly appreciate if you could suggest a similar problem which I can try.

Thanks

Hi sydneyuni2014,

I believe you're referring to the question that starts at 3:00 in this video https://www.gmatprepnow.com/module/gmat ... video/1103

The important concept here is that statements 1 and 2 LOCK the length of AB into having just one measurement, which means the combined statements are sufficient. Since this is a Data Sufficiency Question, we need not actually find the length of AB; we need only recognize that if we were to attempt to find that length, our calculations would reveal that there is ONLY ONE possible length of AB.

If we were to try to find the length of AB, one possible approach would be to physically DRAW the figure (using rulers and protractors) and then just measure AB (many will find this approach unsatisfying )

Another approach is to apply some geometric properties.
Here's the diagram in question:


I'll give you a hint: draw a line from point E down to the side AC so that this line is perpendicular to side AC. This will create two 30-60-90 triangles.

RELATED VIDEO
Special Right Triangles - https://www.gmatprepnow.com/module/gmat ... /video/870