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
we will pick new questions that match your level based on your Timer History
Track Your Progress
every week, we’ll send you an estimated GMAT score based on your performance
Practice Pays
we will pick new questions that match your level based on your Timer History
Not interested in getting valuable practice questions and articles delivered to your email? No problem, unsubscribe here.
Thank you for using the timer!
We noticed you are actually not timing your practice. Click the START button first next time you use the timer.
There are many benefits to timing your practice, including:
Join our live webinar and learn how to approach Data Sufficiency and Critical Reasoning problems, how to identify the best way to solve each question and what most people do wrong.
From Dec 5th onward, American programs will start releasing R1 decisions. Chat Rooms: We have also assigned chat rooms for every school so that applicants can stay in touch and exchange information/update during decision period.
but if we solve it like this: subtract x+y < 20 y < 20
x+y-y<0 x<0
then x will be certainly less than 20...
Why is this approach flawed ?
Bunuel wrote:
enigma123 wrote:
Is x < 20?
1. Sum of x and y is less than 20
2. y is less than 20
How come the answer is E and not A?
Consider two cases: x=30 and y=-15; x=15 and y=-15;
Both examples satisfy the statements and give different answers to the question whether x<20. Not sufficient.
Answer: E.
That's wrong because you cannot subtract inequalities with signs in the same direction.
ADDING/SUBTRACTING INEQUALITIES:
You can only add inequalities when their signs are in the same direction:
If \(a>b\) and \(c>d\) (signs in same direction: \(>\) and \(>\)) --> \(a+c>b+d\). Example: \(3<4\) and \(2<5\) --> \(3+2<4+5\).
You can only apply subtraction when their signs are in the opposite directions:
If \(a>b\) and \(c<d\) (signs in opposite direction: \(>\) and \(<\)) --> \(a-c>b-d\) (take the sign of the inequality you subtract from). Example: \(3<4\) and \(5>1\) --> \(3-5<4-1\).
Question about DS - Is x less than 20?
[#permalink]
Show Tags
21 Jul 2014, 15:55
Hi All,
I have a question regarding a data sufficiency problem.
Is x less than 20?
1) x + y < 20 2) y is less than 20
My question refers to 1.). In this case, since it says x + y, can we plug in a negative number in for y even with a + sign in front of it?
ex. if x=25, y=-8, 25 + (-8) = 17 we do not know if x<20, therefore INSUFFICIENT
I am sure this question is pretty basic to most, but it is these small details that seem to throw me off while solving DS problems. Any advice would be very helpful.
BTW - This question is from the CAT on GMATPrep software.
I have a question regarding a data sufficiency problem.
Is x less than 20?
1) x + y < 20 2) y is less than 20
My question refers to 1.). In this case, since it says x + y, can we plug in a negative number in for y even with a + sign in front of it?
ex. if x=25, y=-8, 25 + (-8) = 17 we do not know if x<20, therefore INSUFFICIENT
I am sure this question is pretty basic to most, but it is these small details that seem to throw me off while solving DS problems. Any advice would be very helpful.
BTW - This question is from the CAT on GMATPrep software.
Thanks, Mike
Merging similar topics. Please refer to the discussion above.
As for your question: y is some number, it could be negative, positive or 0. So, you can plug any number you want there.
say x=5, y=14, sum is 19. so x+y < 20. Also x is less than 20.
Now take x=25, y=-16, sum is 9. so x+y < 20. BUT x is more than 20.
So not sufficient
Statement 2 This statement does not say anything about x. Clearly Not sufficient.
Combining Statements 1 and 2
Our above examples will suit the purpose, as in both cases y is less than 20.
say x=5, y=14, sum is 19. so x+y < 20. Also y is less than 20. Here x is less than 20 Now take x=25, y=-16, sum is 9. so x+y < 20. Also y < 20. BUT x is more than 20.
Is x less than 20 ? (1) The sum of x and y is less than 20. (2) y is less than 20.
Solution:
Answer should be E. Here it is how:
1: x+y < 20 ---> tells us nothing about y or x. say x=24, y= -10 then x < 20 No. Say x = 17 y =1 then x <20 Yes. --- > Insufficient. 2: y <20 , nothing is told about x. ----> clearly insufficient.
Combined. x+y < 20 and y <20. Again, use the example given in statement 1. If x=24, y= -10 then x < 20 No. If x = 17, y =1 then x <20 Yes.
(1) The sum of x and y is less than 20. (2) y is less than 20.
(1) The sum of x and y is less than 20. x+y<20 ; infinite possible values of x ; NOT SUFFICIENT
(2) y is less than 20 Doesn't even talk about x; NOT SUFFICIENT
MERGING x+less than 20<20 Case 1 ) Y is negative x+(-30)<20 ==> x<50 {{{ Is x less than 20? = NO}}}
Case 1 ) Y is Positive x+14<20 ==> x<6 {{{Is x less than 20? =YES}}}
NOT SUFFICIENT
ANSWER SHOULD BE E
_________________
Posting an answer without an explanation is "GOD COMPLEX". The world doesn't need any more gods. Please explain you answers properly. FINAL GOODBYE :- 17th SEPTEMBER 2016. .. 16 March 2017 - I am back but for all purposes please consider me semi-retired.
Statement 1: (x + y) < 20 Possible combinations, 1. x = 50, y = -10 2. x = 10, y = 5 so, value of x can be more than 20 or less than 20 we don't know about that.
Thanks to another GMAT Club member, I have just discovered this valuable topic, yet it had no discussion for over a year. I am now bumping it up - doing my job. I think you may find it valuable (esp those replies with Kudos).
Want to see all other topics I dig out? Follow me (click follow button on profile). You will receive a summary of all topics I bump in your profile area as well as via email.
_________________
close
80% (00:55) correct 
