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Need Help Solving a problem

by psavalia » Thu May 22, 2014 1:42 pm
The following is DS question from Kaplan Premier 2014 on page 699.

What is the value of integer n?

(1) n = n^4
(2) 1^n does not equal 0

** Insert Standard DS option choices here**

I came to the conclusion that the answer is B. Only statement 2 is sufficient. However the book claims its C; Both statements together are sufficient.
My logic behind this is statement 1 is insufficient because it yields 1 or 0 as possible answers. However in statement 2 only 0 can be the answer thus making it sufficient as 1^0 = 1 and 1 does not equal 0. Whats your take on it guys?
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by Brent@GMATPrepNow » Thu May 22, 2014 1:51 pm
psavalia wrote: What is the value of integer n?

(1) n = n^4
(2) 1^n does not equal 0
Are you sure you transcribed the question correctly??
1^n can never equal 0, so statement 2 tells us nothing.

If you correctly transcribed, then the answer is actually E

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by psavalia » Thu May 22, 2014 1:59 pm
Good catch Brent, you are right I did transcribe it wrong. Statement 2 should read: "1^n does not equal n"

so...

(1) n = n^4
(2) 1^n does not equal n
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by Brent@GMATPrepNow » Thu May 22, 2014 2:13 pm
psavalia wrote: What is the value of integer n?

(1) n = n^4
(2) 1^n does not equal n
Target question: What is the value of integer n?

Given: n is an integer

Statement 1: n = n^4
There are two values of n that satisfy this equation.
Case a: n = 0
Case b: n = 1
Since we cannot answer the target question with certainty, statement 1 is NOT SUFFICIENT

Statement 2: 1^n does not equal n
There are several values of n that satisfy this condition. Here are three:
Case a: n = 0
Case b: n = 2
Case c: n = 3 etc...[Aside: statement 2 essentially tells us that n ≠ 1]
Since we cannot answer the target question with certainty, statement 2 is NOT SUFFICIENT


Statements 1 and 2 combined
Statement 1 tells us that n = 0 OR n = 1
Statement 2 tells us that n ≠ 1
So, it MUST BE THE CASE that n = 0
Since we can answer the target question with certainty, the combined statements are SUFFICIENT

Answer = C

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by ceilidh.erickson » Mon May 26, 2014 8:02 am
psavalia wrote: I came to the conclusion that the answer is B. Only statement 2 is sufficient. However the book claims its C; Both statements together are sufficient.
My logic behind this is statement 1 is insufficient because it yields 1 or 0 as possible answers. However in statement 2 only 0 can be the answer thus making it sufficient as 1^0 = 1 and 1 does not equal 0. Whats your take on it guys?
[/list][/i]
It sounds to me like you have fallen prey to STATEMENT CARRYOVER. You were taking the information you had gotten from statement 1 and applying it to statement 2 without evaluating statement 2 by itself.

In statement 2, 1^n does not equal n could be true for an infinite number of values:
1^2 does not equal 2.
1^-5 does not equal 5.
etc.

In fact, the only thing that statement 2 tells us is that n is not equal to 1.

Be very wary of statement carryover - do you often find yourself picking B when the answer should have been C? I will often have my students cross out whatever they wrote down for statement 1 before reading statement 2 to avoid this problem.
Ceilidh Erickson
EdM in Mind, Brain, and Education
Harvard Graduate School of Education
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by ceilidh.erickson » Mon May 26, 2014 8:03 am
For more on STATEMENT CARRYOVER, see:
https://www.beatthegmat.com/gmat-og-13-t ... tml#653748
Ceilidh Erickson
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Harvard Graduate School of Education
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by Brent@GMATPrepNow » Mon May 26, 2014 1:27 pm
As Ceilidh notes, STATEMENT CARRYOVER is a very common mistake that students make when they begin tackling Data Dufficiency questions.

This and several other common Data Sufficiency (DS) mistakes are covered in our free videos:
- Common Data Sufficiency mistakes - part I: https://www.gmatprepnow.com/module/gmat- ... cy?id=1097
- Common Data Sufficiency mistakes - part II: https://www.gmatprepnow.com/module/gmat- ... cy?id=1105

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