Bunuel

In the figure above, is AB > BC? (Note: Figure not necessarily drawn to scale.)
(1) AB > CD
(2) (AD − AB) > (AD − BC)
Attachment:
2016-08-23_1343.png
Target question: Is AB > BC? Statement 1: AB > CD This statement doesn't FEEL sufficient, so I'll TEST some values.
There are several scenarios that satisfy statement 1. Here are two:
Case a: AB = 3, BC = 1, and CD = 1. In this case,
AB > BCCase b: AB = 3, BC = 4, and CD = 1. In this case,
AB < BCSince we cannot answer the
target question with certainty, statement 1 is NOT SUFFICIENT
Aside: For more on this idea of plugging in values when a statement doesn't feel sufficient, you can read my article: https://www.gmatprepnow.com/articles/dat ... lug-values Statement 2: (AD − AB) > (AD − BC)Take AD − AB > AD − BC
Subtract AD from both sides to get: -AB > -BC
Multiply both sides by -1 to get:
AB < BCPERFECT!!
Since we can answer the
target question with certainty, statement 2 is SUFFICIENT
Aside: notice that when we multiplies both sides by -1, we REVERSED the direction of the inequality symbol. Answer =
RELATED VIDEO