BREAKING: Target Test Prep releases Brand New 2026 On Demand GMAT prep course

Redeem

Is x + y < 1 ?

This topic has expert replies
Post new topic Post Reply
Previous Topic Next Topic
Newbie | Next Rank: 10 Posts
Posts: 3
Joined: Sat Sep 13, 2008 7:52 am

Is x + y < 1 ?

by asht » Mon Mar 09, 2009 6:23 am
Is x + y < 1 ?

1. x < 8/9
2. y < 1/8

I answered C, but unfortunately it was shown as wrong. The given OA answer didn't make any sense to me. Pls help!

OA is E
Last edited by asht on Mon Mar 09, 2009 6:41 am, edited 1 time in total.
Top
Source: — Data Sufficiency |
User avatar
Site Admin
Posts: 2567
Joined: Thu Jan 01, 2009 10:05 am
Thanked: 712 times
Followed by:550 members
GMAT Score:770

by DanaJ » Mon Mar 09, 2009 6:29 am
Each stmt by itself is obviously insufficient, since we need to know info about both x and y to solve the problem. Now, take them both together:
1. -x < 8/9 makes x > -8/9
2. -y < 1/8 makes y > -1/8

Now, as you can see, this info is not enough as well. Consider x = y = 0: this means that indeed x + y < 1. But, if you take say x = 2 and y = 1, then x + y > 1.
This is why the OA is E
Top
Junior | Next Rank: 30 Posts
Posts: 26
Joined: Thu Apr 03, 2008 1:20 pm
Thanked: 6 times

by praxis » Mon Mar 09, 2009 6:31 am
When you multiply an inequality by a negative number, the sense of the inequality is reversed. For example, take " x < 1 ". Multiply by -1, and reverse the sense to get " -x > -1 ", not " -x < -1 ".

(1) subtract 1, and multiply by -1 to get
x > 1/9
(2) subtract 2, and multipy by -1 to get
y > 15/8

I think they're sufficient together. What is the source? Perhaps there's a typo in the question or your posting?
Want more practice GMAT questions? check out
https://www.testsandtutors.com/course/view.php/GMAT
Top
Junior | Next Rank: 30 Posts
Posts: 26
Joined: Thu Apr 03, 2008 1:20 pm
Thanked: 6 times

by praxis » Mon Mar 09, 2009 6:38 am
Hah, I read the (1) and (2) in the question as part of the equations.

Pretend I said what DanaJ said.

Moving right along....
Want more practice GMAT questions? check out
https://www.testsandtutors.com/course/view.php/GMAT
Top
Newbie | Next Rank: 10 Posts
Posts: 3
Joined: Sat Sep 13, 2008 7:52 am

Ques edited

by asht » Mon Mar 09, 2009 6:43 am
Hi DanaJ, its not -x.

I have edited the ques, the hyphen was misconstrued as -ve sign
DanaJ wrote:Each stmt by itself is obviously insufficient, since we need to know info about both x and y to solve the problem. Now, take them both together:
1. -x < 8/9 makes x > -8/9
2. -y < 1/8 makes y > -1/8

Now, as you can see, this info is not enough as well. Consider x = y = 0: this means that indeed x + y < 1. But, if you take say x = 2 and y = 1, then x + y > 1.
This is why the OA is E
Top
Newbie | Next Rank: 10 Posts
Posts: 3
Joined: Sat Sep 13, 2008 7:52 am

Source is GmatPrep

by asht » Mon Mar 09, 2009 6:44 am
The source of Ques and OA is GMAT Prep
Top
User avatar
Site Admin
Posts: 2567
Joined: Thu Jan 01, 2009 10:05 am
Thanked: 712 times
Followed by:550 members
GMAT Score:770

by DanaJ » Mon Mar 09, 2009 6:49 am
OK then, let's look at it again:
So you have that x < 8/9 and y < 1/8. The trick here is to notice that y is smaller than 1/8 INSTEAD of 1/9. If you had that:
x < 8/9
y < 1/9
--------
x + y would indeed be smaller than 1.
But since 1/8 > 1/9, you get that there is a small chance that y might be in that interval between 1/9 and 1/8. Look at this:
x < 8/9
y < 1/8
--------
x + y < 8/9 + 1/8 or x + y < 73/72.
It's that small portion of (73/72 - 1) = 1/72 that gives you the headache.
This is why I'm sticking by my answer.
Top
Master | Next Rank: 500 Posts
Posts: 139
Joined: Wed Oct 22, 2008 4:36 am
Thanked: 17 times

by sacx » Tue Mar 10, 2009 4:28 am
it is easier to convert it into decimals and then solve

x < 8/9 ~0.888
y < 1/8 ~0.125

Case I: now lets suppose x = 0.887 and y = 0.124

x +y = 1.011 >1

Case I: now lets suppose x = 0.6 and y = 0.1

x +y = 0.7 <1

Hence the answer should be E
SACX
Top
Legendary Member
Posts: 2789
Joined: Tue Jul 26, 2011 12:19 am
Location: Chennai, India
Thanked: 206 times
Followed by:43 members
GMAT Score:640

by GmatKiss » Tue Oct 04, 2011 6:15 am
asht wrote:Is x + y < 1 ?

1. x < 8/9
2. y < 1/8

I answered C, but unfortunately it was shown as wrong. The given OA answer didn't make any sense to me. Pls help!

OA is E
Lets plug in values,

1) X should be 0.888888888888887 or lesser
2) Y should be 0.1025 or lesser

1+2) x+y = 1.013, which is greater than 1 (max value)
1+2) x+y = 0.001+0.001 = 0.002, which is less than 1

So insufficient!

IMO:E
Top
Post new topic Post Reply
• Page 1 of 1