Bunuel
Is the sum of x, y, and z equal to 3?
(1) xyz = 1
(2) x, y, and z are each greater than zero.
Target question: Is the sum of x, y, and z equal to 3? Statement 1: xyz = 1 This statement doesn't FEEL sufficient, so I'll TEST some values.
There are several values of x, y and z that satisfy statement 1. Here are two:
Case a: x = 1, y = 1 and z = 1, in which case
x + y + z = 1 + 1 + 1 = 3Case b: x = 1, y = 0.5 and z = 2, in which case
x + y + z = 1 + 0.5 + 2 = 3.5Since 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, read my article: https://www.gmatprepnow.com/articles/dat ... lug-values Statement 2: x, y, and z are each greater than zero There are several values of x, y and z that satisfy statement 2. Here are two:
Case a: x = 1, y = 1 and z = 1, in which case
x + y + z = 1 + 1 + 1 = 3Case b: x = 1, y = 0.5 and z = 2, in which case
x + y + z = 1 + 0.5 + 2 = 3.5Since we cannot answer the
target question with certainty, statement 2 is NOT SUFFICIENT
Statements 1 and 2 combined IMPORTANT: Notice that I was able to use the
same counter-examples to show that each statement ALONE is not sufficient. So, the same counter-examples will satisfy the two statements COMBINED.
In other words,
Case a: x = 1, y = 1 and z = 1, in which case
x + y + z = 1 + 1 + 1 = 3Case b: x = 1, y = 0.5 and z = 2, in which case
x + y + z = 1 + 0.5 + 2 = 3.5Since we cannot answer the
target question with certainty, the combined statements are NOT SUFFICIENT
Answer:
Cheers,
Brent