Is X + Y < 1 ?
1. X < 8 / 9
2. Y < 1 / 8
I picked C, but the answer is E
If you give both numbers a common denominator, you get
1) X< 64/72
2) Y< 9/72
Obviously, each statement alone is insufficient. But I'm confused why together they don't work. Since X must be less than 64/72, the largest it can be is 63/72. And since Y is less than 9/72, the largest it can be is 8/72. Together, their maximum values add up to 71/72, which is less than 1. Why can't you definitively say that X + Y < 1?
5-Day Free Trial
5-day free, full-access trial TTP
Available with Beat the GMAT members only code
MORE DETAILS
GMAT PREP QUESTION
This topic has expert replies
-
Stockmoose16
- Master | Next Rank: 500 Posts
- Posts: 347
- Joined: Mon Aug 04, 2008 1:42 pm
- Thanked: 1 times
-
logitech
- Legendary Member
- Posts: 2134
- Joined: Mon Oct 20, 2008 11:26 pm
- Thanked: 237 times
- Followed by:25 members
- GMAT Score:730
BE VERY CAREFUL!Stockmoose16 wrote:Is X + Y < 1 ?
1. X < 8 / 9
2. Y < 1 / 8
I picked C, but the answer is E
If you give both numbers a common denominator, you get
1) X< 64/72
2) Y< 9/72
Obviously, each statement alone is insufficient. But I'm confused why together they don't work. Since X must be less than 64/72, the largest it can be is 63/72. And since Y is less than 9/72, the largest it can be is 8/72. Together, their maximum values add up to 71/72, which is less than 1. Why can't you definitively say that X + Y < 1?
x<1
y<2
means, x+y<3
Think them together!
so
X < 8 / 9
Y < 1 / 8
X+Y < 73/72
Hence, E
LGTCH
---------------------
"DON'T LET ANYONE STEAL YOUR DREAM!"
---------------------
"DON'T LET ANYONE STEAL YOUR DREAM!"
-
cramya
- Legendary Member
- Posts: 2467
- Joined: Thu Aug 28, 2008 6:14 pm
- Thanked: 331 times
- Followed by:11 members
Stockmoose,
I think since the inequalities face the same direction u can add like u said before in one of ur posts
x+y < 73/72 like Logitech said and we dont know if its between 1.0 and 1.01 which would make it > 1 ot rit could be <1 we dont know
INSUFF since we cant come to a definite yes or no
hence E
I think since the inequalities face the same direction u can add like u said before in one of ur posts
x+y < 73/72 like Logitech said and we dont know if its between 1.0 and 1.01 which would make it > 1 ot rit could be <1 we dont know
INSUFF since we cant come to a definite yes or no
hence E
-
scoobydooby
- Legendary Member
- Posts: 1035
- Joined: Wed Aug 27, 2008 10:56 pm
- Thanked: 104 times
- Followed by:1 members
But I'm confused why together they don't work. Since X must be less than 64/72, the largest it can be is 63/72. And since Y is less than 9/72, the largest it can be is 8/72. Together, their maximum values add up to 71/72, which is less than 1. Why can't you definitively say that X + Y < 1?[/quote]
x could well be 63.5/72 and y could be 8.5/72, and if you add you can get 72/72=1 so x+y not neccessary less than 1
x could well be 63.5/72 and y could be 8.5/72, and if you add you can get 72/72=1 so x+y not neccessary less than 1
-
lilu
- Master | Next Rank: 500 Posts
- Posts: 148
- Joined: Wed Dec 10, 2008 5:13 pm
- Location: SF, CA
- Thanked: 12 times
I'd like to pull this thread up and see if any of the experts can comment on this problem.
I have the same confusion as scoobydooby has because I think that the problem states that values need to be LESS than 8/9 and 1/8 and if we take the closest values (but less) to these, we get a value less than 1.....
Shouldn't C be the answer?
I have the same confusion as scoobydooby has because I think that the problem states that values need to be LESS than 8/9 and 1/8 and if we take the closest values (but less) to these, we get a value less than 1.....
Shouldn't C be the answer?
The more you look, the more you see.
GMAT/MBA Expert
-
Ian Stewart
- GMAT Instructor
- Posts: 2621
- Joined: Mon Jun 02, 2008 3:17 am
- Location: Montreal
- Thanked: 1090 times
- Followed by:355 members
- GMAT Score:780
No, the answer is E. Using both statements, we know thatlilu wrote:I'd like to pull this thread up and see if any of the experts can comment on this problem.
I have the same confusion as scoobydooby has because I think that the problem states that values need to be LESS than 8/9 and 1/8 and if we take the closest values (but less) to these, we get a value less than 1.....
Shouldn't C be the answer?
X < 8 / 9
Y < 1 / 8
It's perfectly fine to add inequalities as long as they face the same way, so we have
X < 64/72
Y < 9/72
X+Y < 73/72
That's all we can conclude from the information given, and X+Y can certainly be somewhere between 1 and 73/72. There's no reason why X can't be just slightly less than 64/72 here - X could be 63.9/72 = 639/720, for example. Y could also be just slightly less than 9/72; Y could be 8.9/72 = 89/720. Then X+Y = 639/720 + 89/720 = 728/720, which is greater than 1.
For online GMAT math tutoring, or to buy my higher-level Quant books and problem sets, contact me at ianstewartgmat at gmail.com
ianstewartgmat.com
ianstewartgmat.com
