Find all School-related info fast with the new School-Specific MBA Forum

 It is currently 03 May 2015, 01:59

### GMAT Club Daily Prep

#### Thank you for using the timer - this advanced tool can estimate your performance and suggest more practice questions. We have subscribed you to Daily Prep Questions via email.

Customized
for You

we will pick new questions that match your level based on your Timer History

Track

every week, we’ll send you an estimated GMAT score based on your performance

Practice
Pays

we will pick new questions that match your level based on your Timer History

# Events & Promotions

###### Events & Promotions in June
Open Detailed Calendar

# What is the value of a^4-b^4? 1) a^2 - b^2 = 16 2) a + b = 8

Author Message
TAGS:
Manager
Joined: 30 Oct 2004
Posts: 137
Followers: 1

Kudos [?]: 15 [0], given: 0

What is the value of a^4-b^4? 1) a^2 - b^2 = 16 2) a + b = 8 [#permalink]  22 Dec 2004, 23:32
00:00

Difficulty:

(N/A)

Question Stats:

0% (00:00) correct 0% (00:00) wrong based on 1 sessions
What is the value of a^4-b^4?

1) a^2 - b^2 = 16

2) a + b = 8
Manager
Joined: 30 Oct 2004
Posts: 137
Followers: 1

Kudos [?]: 15 [0], given: 0

The OA is C, which I disagree with.

a^2 - b^2 = 16
(a-b)(a+b)=16

While attempting the problem, I tried a few combinations of numbers and figured out that a=5 and b=3.

Possibilities are: 1 * 16, 2*8, 4*4. But only 2*8 would work here for the equation to make sense.

So for the answer, I put A.
Manager
Joined: 29 Jul 2004
Posts: 62
Followers: 1

Kudos [?]: 0 [0], given: 0

Questor wrote:
The OA is C, which I disagree with.

a^2 - b^2 = 16
(a-b)(a+b)=16

While attempting the problem, I tried a few combinations of numbers and figured out that a=5 and b=3.

Possibilities are: 1 * 16, 2*8, 4*4. But only 2*8 would work here for the equation to make sense.

So for the answer, I put A.

What about a= -5 and b=-3? I think you need statement 2.
Senior Manager
Joined: 19 Sep 2004
Posts: 371
Followers: 1

Kudos [?]: 3 [0], given: 0

Exactly!
Same mistake I made when I was solving problem.

My suggestion to you as SOON as you SPOT a EVEN power. KICK yourself and say "I HAVE TO CHECK -VE NUMBERS ALSO"

Thats how I learnt. Otherwise I always forget to check the -ve numbers.

Thanks
Saurabh Malpani
Manager
Joined: 30 Oct 2004
Posts: 137
Followers: 1

Kudos [?]: 15 [0], given: 0

Re: DS #250 [#permalink]  23 Dec 2004, 10:37
Good point, toddmartin! Thanks!

Even though plugging in numbers could be helpful for solving problems like this one, this strategy can very time consuming (and costly if one forgets to plug in a key set of numbers). While going through the OG, I found that ETS prefers to manipulate equations in clever ways instead. I guess we need to put ourselves in ETS's frame of mind.
Re: DS #250   [#permalink] 23 Dec 2004, 10:37
Similar topics Replies Last post
Similar
Topics:
6 What is the value of a^4 - b^4 ? 3 04 Sep 2009, 16:56
What is the value of a^4 - b^4? 1) a^2 - b^2 = 16 2) a + b = 3 25 Nov 2007, 15:06
What is the value of a^4 - b^4? (1) a^2 - b^2 = 16 (2) a + b 6 23 Aug 2007, 16:55
What is the value of a^4 - b^4 ? 1) a^2 - b^2 = 16 2) a+b = 2 22 Dec 2006, 08:20
5 What is the value of a^4 - b^4 ? 3 25 Nov 2005, 08:43
Display posts from previous: Sort by