|
|
GMAT Club Daily Prep
Thank you for using the timer - this advanced tool can estimate your performance and suggest more practice questions. We have subscribed you to Daily Prep Questions via email.
Customized
for You
Track
Your Progress
Practice
Pays
Not interested in getting valuable practice questions and articles delivered to your email? No problem, unsubscribe here.
11 Oct 2019, 01:50
Kudos
Bookmarks
E
Be sure to select an answer first to save it in the Error Log before revealing the correct answer (OA)!
Difficulty:
5%
(low)
Question Stats:
87% (00:58) correct
13%
(00:56)
wrong
based on 105
sessions
History
Date
Time
Result
Not Attempted Yet
Is the sum of the integers x and y a prime number?
(1) x is an even prime number.
(2) y is a prime number between 10 and 20.
(1) x is an even prime number.
(2) y is a prime number between 10 and 20.
siddharthkapoor
GMAT Club Reviews PM Intern
Joined: 10 Apr 2018
Last visit: 12 Sep 2025
Posts: 527
Given Kudos: 522
Location: India
Schools: ISB'22 (D)
GMAT 1: 680 Q48 V34
GPA: 3.3
Products:
11 Oct 2019, 08:59
Kudos
Bookmarks
We are required to check whether x+y is a prime number.
(1) 2 is the only even prime number, so x=2
However, we don't know the value of y.
Thus, insufficient.
(2) As per this statement, y=13,17, or 19.
Also, we don't know the value of x.
Thus, insufficient.
From (1) and (2) together, x+y=15,19,or 21.
Thus, insufficient.
Therefore, answer is option E.
(1) 2 is the only even prime number, so x=2
However, we don't know the value of y.
Thus, insufficient.
(2) As per this statement, y=13,17, or 19.
Also, we don't know the value of x.
Thus, insufficient.
From (1) and (2) together, x+y=15,19,or 21.
Thus, insufficient.
Therefore, answer is option E.
11 Oct 2019, 09:26
Kudos
Bookmarks
Bunuel
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.
Since we have 2 variables (x and y) and 0 equations, C 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)
If x = 2 and y = 11, then x + y = 13 is a prime number and the answer is 'yes'.
If x = 2 and y = 13, then x + y = 15 is not a prime number and the answer is 'no'.
Since both conditions together do not yield a unique solution, they are not sufficient.
Therefore, E is the answer.
Normally, in problems which require 2 equations, such as those in which the original conditions include 2 variables, or 3 variables and 1 equation, or 4 variables and 2 equations, each of conditions 1) and 2) provide an additional equation. In these problems, the two key possibilities are that C is the answer (with probability 70%), and E is the answer (with probability 25%). Thus, there is only a 5% chance that A, B, or D is the answer. This occurs in common mistake types 3 and 4. Since C (both conditions together are sufficient) is the most likely answer, we save time by first checking whether conditions 1) and 2) are sufficient, when taken together. Obviously, there may be cases in which the answer is A, B, D, or E, but if conditions 1) and 2) are NOT sufficient when taken together, the answer must be E.
