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og ds 137

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Source: — Data Sufficiency |
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Re: og ds 137

by dally_gmat » Sat Oct 25, 2008 7:32 pm
2nd Statement says a= b = 8, So we know for sure a^4 = 8^4 = B^4 therefore b should be sufficient.

1st statement does not answer the question, hence insufficient.

Where I am going wrong?
simba12123 wrote:what is the value of (a^4) - (b^4)?

1. (a^2) - (b^2) = 16

2. a=b=8

qa is c

however cant see to get the meaning of (a^2)+(b^2)
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by rohangupta83 » Sun Oct 26, 2008 1:46 am
i concur with dally_gmat

second statement should be sufficient

a^4 - b^4 upon simplifying gives us

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

a=b=8

will give us
(a-b)(a+b)(a^2+b^2) = 0

imo B
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Re: og ds 137

by reacher » Sun Oct 26, 2008 5:55 am
simba12123 wrote:what is the value of (a^4) - (b^4)?

1. (a^2) - (b^2) = 16

2. a=b=8

qa is c

however cant see to get the meaning of (a^2)+(b^2)
You seem to have changed the statement 2 of the question simba. Statement 2 actually reads " a+b=8 " and with this statement one can solve only a part of the answer and thus combining the statements gets the answer C.
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