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

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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
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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
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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
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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
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by crackgmat007 » Sat Jun 20, 2009 7:43 am
thanks all..it was an easy one (using more plugins should have helped)
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