GMAT PREP QUESTION

Expert replies

Stockmoose16: Master | Next Rank: 500 Posts; Posts: 347; Joined: Mon Aug 04, 2008 1:42 pm; Thanked: 1 times

by Stockmoose16 » Tue Nov 04, 2008 8:34 pm

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?

Like this post

Source: Beat The GMAT — Data Sufficiency | Tue Nov 04, 2008 8:34 pm

jayjk78: Junior | Next Rank: 30 Posts; Posts: 17; Joined: Mon Sep 22, 2008 7:27 am

by jayjk78 » Tue Nov 04, 2008 8:45 pm

8/9 = 0.8888 lets round it (remember 1/9 = 0.111)
1/8= 0.125

without rounding it to two decimals there is still scope for it to equal to 1 or below. hence both statement are not suff.

Like this post

logitech: Legendary Member; Posts: 2134; Joined: Mon Oct 20, 2008 11:26 pmFollowed by: 25 members; Thanked: 237 times; GMAT Score:730

Re: GMAT PREP QUESTION

by logitech » Tue Nov 04, 2008 10:31 pm

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?

BE VERY CAREFUL!

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!"

Like this post

cramya: Legendary Member; Posts: 2467; Joined: Thu Aug 28, 2008 6:14 pmFollowed by: 11 members; Thanked: 331 times

by cramya » Tue Nov 04, 2008 10:35 pm

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

Like this post

scoobydooby: Legendary Member; Posts: 1035; Joined: Wed Aug 27, 2008 10:56 pmFollowed by: 1 member; Thanked: 104 times

Re: GMAT PREP QUESTION

by scoobydooby » Wed Nov 05, 2008 1:20 am

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

Like this post

lilu: Master | Next Rank: 500 Posts; Posts: 148; Joined: Wed Dec 10, 2008 5:13 pm; Location: SF, CA; Thanked: 12 times

by lilu » Fri May 08, 2009 9:29 am

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?

The more you look, the more you see.

Like this post

GMAT/MBA Expert

Ian Stewart: GMAT Instructor; Posts: 2623; Joined: Mon Jun 02, 2008 3:17 amFollowed by: 355 members; Location: Montreal; Thanked: 1090 times; GMAT Score:780

by Ian Stewart » Fri May 08, 2009 3:09 pm

lilu 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?

No, the answer is E. Using both statements, we know that

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

Like this post

Post new topic Post Reply

• Page 1 of 1

GMAT Course Reviews

563 reviews

1168 reviews

431 reviews

359 reviews

147 reviews

5/5

5 Star (563 Reviews)

"Target Test Prep is the closest to the official version of the GMAT exam, about 99% accuracy in terms of the quality and quantity of information. The course has excellently created singular sets of focused lessons and tests for every possible topic that one could come across in the official GMAT exam."

"The TTP course maximizes the efficiency of the time you spend studying. It will take time and effort but I could almost guarantee that if you complete the course exactly as it is laid out you will get an amazing score. They also have a very responsive team willing to help with any questions you might have."

"TTP has two things that I think no other test prep company offers: A teaching approach that reinforces understanding and an attitude that will give you the mental preparedness needed to succeed on the test. TTP gives you a deep understanding of the concept you need to know while teaching you how to think."

Write a Review