functions
This topic has expert replies
Source: Beat The GMAT — Data Sufficiency |
-
Stuart@KaplanGMAT
- GMAT Instructor
- Posts: 3225
- Joined: Tue Jan 08, 2008 2:40 pm
- Location: Toronto
- Thanked: 1710 times
- Followed by:614 members
- GMAT Score:800
Step 1 of the Kaplan method for DS: Analyze the StemGurpinder wrote:If [x] denotes the greatest integer less than or equal to
x, is [x] = 0 ?
(1) 5x + 1 = 3 + 2x
(2) 0 < x < 1
We're told that [x] is the biggest integer less than or equal to x. So, for example, [1.4]=1 (sometimes plugging in numbers helps you understand these wacky functions).
Our question: Is [x]=0?
Yes/no question: if [x] always equals 0, sufficient; if it never equals 0, sufficient. If sometimes it does and sometimes it doesn't, insufficient.
When will [x]=0? If 0 <=x < 1
Step 2 of the Kaplan method for DS: Evaluate the Statements
(1) allows us to calculate an exact value for x. If we can calculate an exact value, we can certainly answer the question: sufficient.
(2) tells us that x is definitely inside the range we defined: sufficient.
Each statement is sufficient alone: choose (D).
Stuart Kovinsky | Kaplan GMAT Faculty | Toronto
Kaplan Exclusive: The Official Test Day Experience | Ready to Take a Free Practice Test? | Kaplan/Beat the GMAT Member Discount
BTG100 for $100 off a full course
-
Gurpinder
- Legendary Member
- Posts: 659
- Joined: Mon Dec 14, 2009 8:12 am
- Thanked: 32 times
- Followed by:3 members
please check if my reasoning is right for picking (D)
Stmt (1)
since you have the equation, we can solve both sides to see if they are equal. if x=0, both sides are not equal. therefore [x] not qual to 0.
so this one is sufficient.
stmt (2)
tells us straight that x is greater than 0, so [x] not equal to zero. therefore this one is sufficient too.
?
Stmt (1)
since you have the equation, we can solve both sides to see if they are equal. if x=0, both sides are not equal. therefore [x] not qual to 0.
so this one is sufficient.
stmt (2)
tells us straight that x is greater than 0, so [x] not equal to zero. therefore this one is sufficient too.
?
"Do not confuse motion and progress. A rocking horse keeps moving but does not make any progress."
- Alfred A. Montapert, Philosopher.
- Alfred A. Montapert, Philosopher.
GMAT/MBA Expert
-
Rahul@gurome
- GMAT Instructor
- Posts: 1179
- Joined: Sun Apr 11, 2010 9:07 pm
- Location: Milpitas, CA
- Thanked: 447 times
- Followed by:88 members
To Gurpinder,
Your reasoning with statement (1) is not correct.
Now [x] = 0 for any value of x such that 0 <= x < 1.
There is no single value of x for which [x] is zero. You are assuming [x] = 0 only if x = 0.
So you have to first solve the equation in statement (1), test whether it is more than or equal to 0 and less than 1 and then decide whether [x] = 0 or not.
Since (1) is giving x as 2/3, [x] = [2/3] = 0.
From statement (2), we have 0 < x < 1. So [x] = 0.
Your conclusion is incorrect for statement (2).
The correct answer is hence (D).
Your reasoning with statement (1) is not correct.
Now [x] = 0 for any value of x such that 0 <= x < 1.
There is no single value of x for which [x] is zero. You are assuming [x] = 0 only if x = 0.
So you have to first solve the equation in statement (1), test whether it is more than or equal to 0 and less than 1 and then decide whether [x] = 0 or not.
Since (1) is giving x as 2/3, [x] = [2/3] = 0.
From statement (2), we have 0 < x < 1. So [x] = 0.
Your conclusion is incorrect for statement (2).
The correct answer is hence (D).
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)
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)
-
Stuart@KaplanGMAT
- GMAT Instructor
- Posts: 3225
- Joined: Tue Jan 08, 2008 2:40 pm
- Location: Toronto
- Thanked: 1710 times
- Followed by:614 members
- GMAT Score:800
I don't often disagree with other GMAT experts, but I'm going to do so here.Rahul@gurome wrote:To Gurpinder,
So you have to first solve the equation in statement (1), test whether it is more than or equal to 0 and less than 1 and then decide whether [x] = 0 or not.
A key to saving time in DS is to do as few calculations as possible. Remember, we don't care what the answer is, we just care whether it's possible to get an answer.
So, you 100% do NOT need (or want) to solve the equation in statement (1). As soon as you see that (1) will generate a precise value for x, you know that it's also possible to get a precise value for [x]. If we can get a precise value for [x], then we can certainly answer the question "does [x]=0?"
How do we know that (1) will generate a precise value for x? We have 1 linear equation and 1 variable, that's how!
Stuart Kovinsky | Kaplan GMAT Faculty | Toronto
Kaplan Exclusive: The Official Test Day Experience | Ready to Take a Free Practice Test? | Kaplan/Beat the GMAT Member Discount
BTG100 for $100 off a full course
-
[email protected]
- Legendary Member
- Posts: 934
- Joined: Tue Nov 09, 2010 5:16 am
- Location: AAMCHI MUMBAI LOCAL
- Thanked: 63 times
- Followed by:14 members
But there are times in DS when you have to do the specific calculations and see whether there is only one specific answer. Especially with the quadratic equations and parabolas.
There are times when in quadratic equations you have 2 roots both positive and both real. Hence the answer is such a case would be insufficient and if you answer it sufficient, you are committing a mistake.
There are times when in quadratic equations you have 2 roots both positive and both real. Hence the answer is such a case would be insufficient and if you answer it sufficient, you are committing a mistake.
IT IS TIME TO BEAT THE GMAT
LEARNING, APPLICATION AND TIMING IS THE FACT OF GMAT AND LIFE AS WELL... KEEP PLAYING!!!
Whenever you feel that my post really helped you to learn something new, please press on the 'THANK' button.
LEARNING, APPLICATION AND TIMING IS THE FACT OF GMAT AND LIFE AS WELL... KEEP PLAYING!!!
Whenever you feel that my post really helped you to learn something new, please press on the 'THANK' button.
