-
kamalakarthi
- Senior | Next Rank: 100 Posts
- Posts: 80
- Joined: Mon Jan 31, 2011 10:08 pm
- Followed by:2 members
Hi ,
Is OA C?
DS5
This topic has expert replies
Source: Beat The GMAT — Data Sufficiency |
-
j_shreyans
- Legendary Member
- Posts: 510
- Joined: Thu Aug 07, 2014 2:24 am
- Thanked: 3 times
- Followed by:5 members
GMAT/MBA Expert
-
[email protected]
- Elite Legendary Member
- Posts: 10392
- Joined: Sun Jun 23, 2013 6:38 pm
- Location: Palo Alto, CA
- Thanked: 2867 times
- Followed by:511 members
- GMAT Score:800
Hi kamalakarthi,
This DS question involves a lot of little steps and a mix of skills (some math skills and TESTing VALUES).
We're told that...
Machine M produces X widgets every 4 minutes
Machine N produces Y widgets every 5 minutes
We're asked if they both word for 20 minutes, does Machine M produce more widgets than Machine N? This is a YES/NO question.
Before we get to the Facts, we can rewrite this question. Over the course of 20 minutes, Machine M will produce 5X widgets and Machine N will produce 4Y widgets, so the question is really asking....
Is 5X > 4Y?
By thinking of these question in these terms, you'll find that the two Facts are considerably easier to deal with.
Fact 1: X > .8Y
This inequality can be simplified with a couple of Algebra steps...
X > .8Y
10X > 8Y
5X > 4Y
Now we KNOW that 5X > 4Y, so no more work is necessary - the answer to the question is ALWAYS YES.
Fact 1 is SUFFICIENT
Fact 2: Y = X+1
This looks like a perfect opportunity to TEST VALUES. From this equation, we know that Y will be 1 greater than X, so the values are "close."
If....
X = 1
Y = 2
Is 5(1) > 4(2)?......Is 5 > 8? The answer is NO
X = 10
Y = 11
Is 5(10) > 4(11)?....Is 50 > 44? The answer is YES
Fact 2 is INSUFFICIENT
Final Answer: A
GMAT assassins aren't born, they're made,
Rich
This DS question involves a lot of little steps and a mix of skills (some math skills and TESTing VALUES).
We're told that...
Machine M produces X widgets every 4 minutes
Machine N produces Y widgets every 5 minutes
We're asked if they both word for 20 minutes, does Machine M produce more widgets than Machine N? This is a YES/NO question.
Before we get to the Facts, we can rewrite this question. Over the course of 20 minutes, Machine M will produce 5X widgets and Machine N will produce 4Y widgets, so the question is really asking....
Is 5X > 4Y?
By thinking of these question in these terms, you'll find that the two Facts are considerably easier to deal with.
Fact 1: X > .8Y
This inequality can be simplified with a couple of Algebra steps...
X > .8Y
10X > 8Y
5X > 4Y
Now we KNOW that 5X > 4Y, so no more work is necessary - the answer to the question is ALWAYS YES.
Fact 1 is SUFFICIENT
Fact 2: Y = X+1
This looks like a perfect opportunity to TEST VALUES. From this equation, we know that Y will be 1 greater than X, so the values are "close."
If....
X = 1
Y = 2
Is 5(1) > 4(2)?......Is 5 > 8? The answer is NO
X = 10
Y = 11
Is 5(10) > 4(11)?....Is 50 > 44? The answer is YES
Fact 2 is INSUFFICIENT
Final Answer: A
GMAT assassins aren't born, they're made,
Rich
-
GMATGuruNY
- GMAT Instructor
- Posts: 15539
- Joined: Tue May 25, 2010 12:04 pm
- Location: New York, NY
- Thanked: 13060 times
- Followed by:1906 members
- GMAT Score:790
Both machines work for the same amount of time.Machine M, working alone at its constant rate, produces x widgets every 4 minutes. Machine N, working alone at its constant rate, produces y widgets every 5 minutes. If machines M and N working simultaneously at their respective constant rates for 20 minutes, does machine M produce more widgets than machine N in that time ?
1) x > 0.8y
2) y = x + 1
To produce more widgets than N, M must work faster than N.
Question rephrased:
Is M faster than N?
Statement 1: x > 0.8y
Let y=10, implying that x>8.
Since y=10, N produces 10 widgets every 5 minutes, implying that N's rate = 10/5 = 2 widgets per minute.
Since x>8, M produces MORE than 8 widgets every 4 minutes, implying that M's rate = (more than 8)/4 = MORE than 2 widgets per minute.
Thus, M is faster than N.
SUFFICIENT.
Statement 2: y = x+1
Case 1: x=1, y=2
Since y=2, N produces 2 widgets every 5 minutes, implying that N's rate = 2/5 widget per minute.
Since x=1, M produces 1 widget every 4 minutes, implying that M's rate = 1/4 widget per minute.
In this case, N is faster than M.
Case 2: x=100, y=101
Since y=101, N produces 101 widgets every 5 minutes, implying that N's rate = 101/5 ≈ 20 widgets per minute.
Since x=100, M produces 100 widgets every 4 minutes, implying that M's rate = 100/4 = 25 widgets per minute.
In this case, M is faster than N.
Since N is faster than M in Case 1 but slower than M in Case 2, INSUFFICIENT.
The correct answer is A.
Private tutor exclusively for the GMAT and GRE, with over 20 years of experience.
Followed here and elsewhere by over 1900 test-takers.
I have worked with students based in the US, Australia, Taiwan, China, Tajikistan, Kuwait, Saudi Arabia -- a long list of countries.
My students have been admitted to HBS, CBS, Tuck, Yale, Stern, Fuqua -- a long list of top programs.
As a tutor, I don't simply teach you how I would approach problems.
I unlock the best way for YOU to solve problems.
For more information, please email me (Mitch Hunt) at [email protected].
Student Review #1
Student Review #2
Student Review #3
Followed here and elsewhere by over 1900 test-takers.
I have worked with students based in the US, Australia, Taiwan, China, Tajikistan, Kuwait, Saudi Arabia -- a long list of countries.
My students have been admitted to HBS, CBS, Tuck, Yale, Stern, Fuqua -- a long list of top programs.
As a tutor, I don't simply teach you how I would approach problems.
I unlock the best way for YOU to solve problems.
For more information, please email me (Mitch Hunt) at [email protected].
Student Review #1
Student Review #2
Student Review #3
