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

Redeem

6 DS answer explanation needed / GMATPrep Test 1

This topic has expert replies
Post new topic Post Reply
Previous Topic Next Topic
Source: — Problem Solving |

GMAT/MBA Expert

User avatar
GMAT Instructor
Posts: 1179
Joined: Sun Apr 11, 2010 9:07 pm
Location: Milpitas, CA
Thanked: 447 times
Followed by:88 members

by Rahul@gurome » Thu Jul 29, 2010 8:00 pm
1st Question:

(1) 2x - 2y = 1 implies x - y = 1/2
Now, if x = 1 and y = 1/2, then x - y = 1/2. Here, x and y are both positive.
If x = 0 and y = -1/2, then x - y = 0 - (-1/2) = 1/2. Here, x and y are not positive.
We don't get a unique answer.
So, (1) is NOT SUFFICIENT.

(2) x/y > 1 implies that either x and y are both positive or x and y are both negative. But this is NOT SUFFICIENT to answer the question again.

Combining (1) and (2), if x = 1 and y = 1/2, then x - y = 1/2. Also x/y > 1 here. If we take negative values for both x and y, then x - y = 1/2 is not satisfied. Hence, x and y can never be negative.
So, answer to the main question is yes.

The correct answer is [spoiler](C)[/spoiler].
Rahul Lakhani
Quant Expert
Gurome, Inc.
https://www.GuroMe.com
On MBA sabbatical (at ISB) for 2011-12 - will stay active as time permits
1-800-566-4043 (USA)
+91-99201 32411 (India)
Top

GMAT/MBA Expert

User avatar
GMAT Instructor
Posts: 1179
Joined: Sun Apr 11, 2010 9:07 pm
Location: Milpitas, CA
Thanked: 447 times
Followed by:88 members

by Rahul@gurome » Thu Jul 29, 2010 8:13 pm
2nd question:

(1) QR = RS implies angle RQS = angle RSQ = y, say.
But, (1) is NOT SUFFICIENT to find x.

(2) ST = TU implies angle TSU = angle SUT = z, say.
But, (2) is NOT SUFFICIENT to find x.

Combining (1) and (2), x + y + z = 180º
Also, angle PRT + angle PTR = 90º (because angle RPT = 90º)

Also, angle PRT = 180 - 2y and angle PTR = 180 - 2z
So, 180 - 2y + 180 - 2z = 90
or y + z = 135, implies x = 180 - 135 = 45º

The correct answer is [spoiler](C)[/spoiler].
Rahul Lakhani
Quant Expert
Gurome, Inc.
https://www.GuroMe.com
On MBA sabbatical (at ISB) for 2011-12 - will stay active as time permits
1-800-566-4043 (USA)
+91-99201 32411 (India)
Top

GMAT/MBA Expert

User avatar
GMAT Instructor
Posts: 1179
Joined: Sun Apr 11, 2010 9:07 pm
Location: Milpitas, CA
Thanked: 447 times
Followed by:88 members

by Rahul@gurome » Thu Jul 29, 2010 8:32 pm
3rd question:

(1) If 8k = 16 then k = 2 and k is not divisible by 4.
If 8k = 32 then k = 4, divisible by 4.
We don't get a unique answer.
So, (1) is NOT SUFFICIENT.

(2) If 9k = 12 then k is not an integer.
If 9k = 24 then also k is not an integer.
If 9k = 36 then k = 4, divisible by 4
If 9k = 48 then also k is not an integer.
If 9k = 60 then also k is not an integer.
If 9k = 72 then k = 8, divisible by 4.

Generalizing, we can say k is divisible by 4 if 9k is divisible by 12.

The correct answer is [spoiler](B)[/spoiler].
Rahul Lakhani
Quant Expert
Gurome, Inc.
https://www.GuroMe.com
On MBA sabbatical (at ISB) for 2011-12 - will stay active as time permits
1-800-566-4043 (USA)
+91-99201 32411 (India)
Top
Master | Next Rank: 500 Posts
Posts: 161
Joined: Mon Apr 05, 2010 9:06 am
Location: Mumbai
Thanked: 37 times

by 4GMAT_Mumbai » Thu Jul 29, 2010 10:06 pm
4th Question:

Even before jumping into statements 1 and 2, let us look at the question.

Time taken if she had done x mph throughout = 40 / x

Time taken in the current scenario = (y/x) + ((40-y)/x)

Ratio of these two = ((y/x) + ((40-y)/x) ) / (40 / x)

It simplifies to (Y + ((40-Y)/1.25))

Stmt 1: Provides info about x. But, not useful as the expression has no x in it.

Stmt 2: Provides info about y. It will help to get a numeric value to the ratio. [spoiler]Hence, sufficient; B[/spoiler]

Hope this helps. Thanks.
Naveenan Ramachandran
4GMAT, Dadar(W) & Ghatkopar(W), Mumbai
Top
Master | Next Rank: 500 Posts
Posts: 161
Joined: Mon Apr 05, 2010 9:06 am
Location: Mumbai
Thanked: 37 times

by 4GMAT_Mumbai » Thu Jul 29, 2010 10:10 pm
5th Question:

Stmt 1:
Let, Rows = C - 1 and Chairs = C

What is given?

C (C-1) = 72

C ^ 2 - C - 72 = 0. Solving this, we get C = 9. Hence, Sufficient.

Stmt 2:

Let Chairs = C

What is given?

C + (C-1) = 17.

C = 9. Hence, Sufficient.

Overall, D

Hope this helps. Thanks.
Naveenan Ramachandran
4GMAT, Dadar(W) & Ghatkopar(W), Mumbai
Top
Master | Next Rank: 500 Posts
Posts: 161
Joined: Mon Apr 05, 2010 9:06 am
Location: Mumbai
Thanked: 37 times

by 4GMAT_Mumbai » Thu Jul 29, 2010 10:15 pm
6th Question:

Statement 1:

x = +1 or -1

But, the question states that x is -ve. Hence, x = 1. Suff

Statement 2:

Solving the equation leads to x = -2 or -1. Hence, Insufficient.

Confused ?!?!? Question you should ask yourself is "Does the statement lead me to be able to provide ONE single answer to the question?" The answer to this question is an YES in the first case and a NO in the second case. This is the reason why the first statement is sufficient and the second is not.

Hope this helps. Thanks.
Naveenan Ramachandran
4GMAT, Dadar(W) & Ghatkopar(W), Mumbai
Top
Post new topic Post Reply
• Page 1 of 1