Comments

1. Mathieu says

   November 4, 2022 at 9:01 AM

   Thanks for this. I thought at statement 1), we have three unknowns and 2 equns, not sufficient. Same for statement 2). Decidedly this was plain wrong. Any way to see quickly whether we can rely or not on this rule of thumb?

   Reply

   • GMAT Quantum says

     November 5, 2022 at 12:55 AM

     There are only two unknowns, x and y, in this question. In the main stem, there is one equation given, and each statement gives an additional equation. The trap answer for this question is D, because the GMAT writers want students to think that because there are two variables, then each statement that provides an additional equation must be sufficient alone. Of course this is a trap.

     I would say in general, I am always careful about using any general rule for number of equations and number of unknowns set ups, because that only works for independent equations, and often that is not the case on the GMAT.

     Here is another classic GMAT example that sets up a similar trap. This one is for a system with three unknowns:

     1. What is the value of $\dfrac{z}{x}$ ?
        
        1. (1) $2x – y + 3z = 5$
        2. (2) $x+ 2y – z = -10$

        1. Statement (1) ALONE is sufficient, but statement (2) alone is not sufficient.
        2. Statement (2) ALONE is sufficient, but statement (1) alone is not sufficient.
        3. BOTH statements TOGETHER are sufficient, but NEITHER statement ALONE is sufficient.
        4. EACH statement ALONE is sufficient.
        5. Statements (1) and (2) TOGETHER are NOT sufficient.
        Choice C

     Reply