Geometry-data sufficiency

[Lavir7]

A Triangle ABC is given with 2 angles : x,y are angles lying across AC and AB ,respectively.

Is triangle ABC isosceles?

1/ X does not equal Y
2/ AB=2BC

The answer given by MGMAT is (C) - both assumptions are needed.
( 1-If x and Y are different it tells us nothing about the third angle AND2- if AB=2BC, BC could still equal AC the )

I think there's a mistake in the answer and the answer is really (B)- meaning that the second piece of information suffices. If AB=2BC and BC+AC must be >AB (triangle rules) , than AC+BC>2BC and AC>BC. i.e. they are not equal and the triangle ABC cannot an isoceles if all sides are different!

Have I reached the wrong conclusion?

[RonPurewal]

A Triangle ABC is given with 2 angles : x,y are angles lying across AC and AB ,respectively.

Is triangle ABC isosceles?

1/ X does not equal Y
2/ AB=2BC

The answer given by MGMAT is (C) - both assumptions are needed.
( 1-If x and Y are different it tells us nothing about the third angle AND2- if AB=2BC, BC could still equal AC the )

I think there's a mistake in the answer and the answer is really (B)- meaning that the second piece of information suffices. If AB=2BC and BC+AC must be >AB (triangle rules) , than AC+BC>2BC and AC>BC. i.e. they are not equal and the triangle ABC cannot an isoceles if all sides are different!

Have I reached the wrong conclusion?

yes.

you are correct in concluding that AC must be greater than BC, but nothing precludes the possibility that AC = AB (i.e., both of them = 2BC). if that is the case, then the triangle will be isosceles.

that's a nice job of manipulating the triangle inequalities, though.

[adityaj123]

Does the questions with answer NO come in real GMAT exam??

[jnelson0612]

Does the questions with answer NO come in real GMAT exam??

adityaj123, definitely! Based on the information in a statement, you absolutely can get an answer of NO for the question, and NO would be sufficient. Yes, we have seen many such instances of that on the real GMAT.