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Data Sufficiency Math Problem

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Intern
Joined: 18 Dec 2009
Posts: 1
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26 Jan 2010, 16:16
What's the value of a^4 - b^4 ?

1. a^2 - b^2 = 16

2. a + b = 8

Appreciate it if somebody can help me in solving the above DS problem. An explanation will also be appreciated.

Thanks
Senior Manager
Joined: 18 Aug 2009
Posts: 328
Followers: 8

Kudos [?]: 268 [1] , given: 13

Re: Data Sufficiency Math Problem [#permalink]

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26 Jan 2010, 16:26
1
KUDOS
What's the value of a^4 - b^4 ?

1. $$a^2 - b^2 = 16$$

2. $$a + b = 8$$

Appreciate it if somebody can help me in solving the above DS problem. An explanation will also be appreciated.

Thanks

IMO C.

$$a^4 - b^4 = (a^2 - b^2)*(a^2 + b^2)$$

1. $$a^2-b^2 = 16$$. Clearly insufficient as we do not know the value of $$a^2+b^2$$.
2. $$a+b = 8$$. Again insufficient as it does not provide any information about value of $$a-b$$.

Together 1 and 2 are sufficient. How???
$$a^2-b^2 = 16$$
$$(a-b)*(a+b) = 16$$
$$a-b = 2$$ As we know that $$a+b = 8$$. Now we can find the value of $$a & b$$.

Re: Data Sufficiency Math Problem   [#permalink] 26 Jan 2010, 16:26
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Data Sufficiency Math Problem

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