What is the value of xy - yz? (1) y = 2 (2) x - z = 5

Question

What is the value of xy - yz?

(1) y = 2

(2) x - z = 5

taniad · Answer

What is the value of xy - yz?

y(x-z)?

(1) y = 2
=> 2(x-z) Not Sufficient.

(2) x - z = 5 
=> y(5) Not Sufficient.

(1)+(2)
xy-yz= y(x-z)= 2(5)= 10 Sufficient

Ans= C

BrentGMATPrepNow · Answer

Important: Notice that we can take xy - yz and factor out the y to get the following equivalent expression: y(x - z)

Target question :    What is the value of y(x - z)?

Statement 1 : y = 2  
Our goal is to determine the value of  y(x - z) 
We now know the value of y, but we don't know the value of (x - z)
Statement 1 is NOT SUFFICIENT

Statement 2 : x - z = 5 
Our goal is to determine the value of  y(x - z) 
We now know the value of (x - z), but we don't know the value of y
Statement 2 is NOT SUFFICIENT

Statements 1 and 2 combined    
Statement 1 tells us that y = 2
Statement 2 tells us that x - z = 5
So,  y(x - z) = 2(5) = 10 
Since we can answer the  target question  with certainty, the combined statements are SUFFICIENT

Answer: C

Cheers,
Brent

Avysar · Answer

The question has three variables. 
A has the value of only y..since we don't have the values of x and z, we cannot find the value of y(x-z). So Insufficient
B gives the value of x-z but not y. So Insufficient.
But together, we can find y(x-z) using both A and B. So C

Posted from my mobile device

MathRevolution · Answer

Forget conventional ways of solving math questions. For DS problems, the VA (Variable Approach) method is the quickest and easiest way to find the answer without actually solving the problem. Remember that equal numbers of variables and independent equations ensure a solution. Visit https://www.mathrevolution.com/gmat/lesson for details. The first step of the VA (Variable Approach) method is to modify the original condition and the question. We then recheck the question. We should simplify conditions if necessary. The question xy - yz is equivalent to y(x-z) by factoring. Since we have 3 variables ( x, y and z ) and 0 equations, E is most likely the answer. So, we should consider conditions 1) & 2) together first. After comparing the number of variables and the number of equations, we can save time by considering conditions 1) & 2) together first. Conditions 1) & 2) xy - yz = y(x-z) = 2 \cdot 5 = 10 since we have y = 2 and x - z = 5 . Since both conditions together yield a unique solution, they are sufficient. Therefore, C is the answer. In cases where 3 or more additional equations are required, such as for original conditions with “3 variables”, or “4 variables and 1 equation”, or “5 variables and 2 equations”, conditions 1) and 2) usually supply only one additional equation. Therefore, there is an 80% chance that E is the answer, a 15% chance that C is the answer, and a 5% chance that the answer is A, B or D. Since E (i.e. conditions 1) & 2) are NOT sufficient, when taken together) is most likely to be the answer, it is generally most efficient to begin by checking the sufficiency of conditions 1) and 2), when taken together. Obviously, there may be occasions on which the answer is A, B, C or D.

bumpbot · Answer

Automated notice from GMAT Club BumpBot: 

A member just gave Kudos to this thread, showing it’s still useful. I’ve bumped it to the top so more people can benefit. Feel free to add your own questions or solutions.

 This post was generated automatically.

What is the value of xy - yz? (1) y = 2 (2) x - z = 5

Prep Toolkit

Top 5 GMAT Debrief Videos

615 to 715 in 15 Days (Ria's Strategies)

More than Quant/Verbal Abilities: Speed vs. Accuracy

745 with Only Self-Prep and GMAT Club

From 555 to 765: 210-point Improvement

Perfect 805 Score Debrief by Julia

My Rewards

GMAT Data Sufficiency (DS) Questions

What is the value of xy - yz? (1) y = 2 (2) x - z = 5

Prep Toolkit

615 to 715 in 15 Days (Ria's Strategies)

More than Quant/Verbal Abilities: Speed vs. Accuracy

745 with Only Self-Prep and GMAT Club

From 555 to 765: 210-point Improvement

Perfect 805 Score Debrief by Julia

My Rewards