What is the value of a^4-b^4

Expert replies

crackgmat007: Legendary Member; Posts: 882; Joined: Fri Feb 20, 2009 2:57 pmFollowed by: 1 member; Thanked: 15 times; GMAT Score:690

by crackgmat007 » Fri Jun 19, 2009 9:55 pm

What is the value of a^4-b^4

1. a^2-b^2=16
2. a+b=8

Pls clarify why statement 1 alone is not sufficient. Using statement 1, i got (a+b)(a-b) = 16. Since (a+b) * (a-b) must result in 16, using plug ins, I got a=5 and b=3.

However, OA - C Pls clarify if I am missing something

Like this post

Source: Beat The GMAT — Data Sufficiency | Fri Jun 19, 2009 9:55 pm

anksgupta: Senior | Next Rank: 100 Posts; Posts: 51; Joined: Wed Apr 29, 2009 9:00 am; Thanked: 6 times

by anksgupta » Fri Jun 19, 2009 10:01 pm

IMO C is right.

YOu need to have 2 equation to solve for a and b

From 1. what if a=4 and b=0 . hence 1. is not enough

using both 1 and 2 , a and b can be calcualted hence C

Live n Love GMAT

Like this post

cramya: Legendary Member; Posts: 2467; Joined: Thu Aug 28, 2008 6:14 pmFollowed by: 11 members; Thanked: 331 times

by cramya » Fri Jun 19, 2009 10:01 pm

a+b = 8
a-b = 2

We get a=5

Lets say a+b=4
a-b=4

we get a=4

2 different values for a^4-b^4

Hence we need both together since we know exactly what a+b so we can clauclate a-b and then the individual values for a and b

Hope this helps.

Regards,
CR

Like this post

greymatter: Newbie | Next Rank: 10 Posts; Posts: 5; Joined: Sat May 30, 2009 2:28 am

Re: What is the value of a^4-b^4

by greymatter » Fri Jun 19, 2009 10:58 pm

crackgmat007 wrote:What is the value of a^4-b^4

1. a^2-b^2=16
2. a+b=8

Pls clarify why statement 1 alone is not sufficient. Using statement 1, i got (a+b)(a-b) = 16. Since (a+b) * (a-b) must result in 16, using plug ins, I got a=5 and b=3.

However, OA - C Pls clarify if I am missing something

how about a =4 and b=0.

answer should be C

Like this post

crackgmat007: Legendary Member; Posts: 882; Joined: Fri Feb 20, 2009 2:57 pmFollowed by: 1 member; Thanked: 15 times; GMAT Score:690

by crackgmat007 » Sat Jun 20, 2009 7:43 am

thanks all..it was an easy one (using more plugins should have helped)

Like this post

Post new topic Post Reply

• Page 1 of 1

GMAT Course Reviews

560 reviews

1168 reviews

431 reviews

359 reviews

147 reviews

5/5

5 Star (560 Reviews)

"Target Test Prep is the closest to the official version of the GMAT exam, about 99% accuracy in terms of the quality and quantity of information. The course has excellently created singular sets of focused lessons and tests for every possible topic that one could come across in the official GMAT exam."

"The TTP course maximizes the efficiency of the time you spend studying. It will take time and effort but I could almost guarantee that if you complete the course exactly as it is laid out you will get an amazing score. They also have a very responsive team willing to help with any questions you might have."

"TTP has two things that I think no other test prep company offers: A teaching approach that reinforces understanding and an attitude that will give you the mental preparedness needed to succeed on the test. TTP gives you a deep understanding of the concept you need to know while teaching you how to think."

Write a Review