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GRE 1: Q166 V156
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Re: If a and b are integers and [#permalink]
Carcass wrote:
If a and b are integers and \(( \sqrt[3]{a} * \sqrt{b} )^6 = 500\), the \(a + b\) could equal

A. 2

B. 3

C. 4

D. 5

E. 6


(a^1/3 * b^1/2)^6 = a^2 * b^3 = 500

500 = 5 * 100 = 5 * 10 * 10 = 5 * 2 * 5 * 2 * 5 = 2^2 * 5*^3




2^2 * 5^3 = 4 * 125 = 500

a = -2 or 2

2 + 5 = 7 or -2 + 5 = 3

Answer choice B
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Re: If a and b are integers and [#permalink]
is it from the book?
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Re: If a and b are integers and [#permalink]
thanks alot
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If a and b are integers and [#permalink]
Expert Reply
If \(a\) and \(b\) are integers and \(( \sqrt[3]{a} * \sqrt{b} )^6 = 500\), then \(a + b\) could equal

A. 2

B. 3

C. 4

D. 5

E. 6
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Re: If a and b are integers and [#permalink]
1
Expert Reply
distribute the exponents, and you get

a^2*b^3 =500
start with a=2, then 2^2*b^3=500
4b^3=500
b^3=125
b=5
but a=b =2+5=7...no option for 7 there.
set a = (-2)
then -2+5=3

the answer is B
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Re: If a and b are integers and [#permalink]
Expert Reply
Carcass wrote:
If \(a\) and \(b\) are integers and \(( \sqrt[3]{a} * \sqrt{b} )^6 = 500\), then \(a + b\) could equal

A. 2

B. 3

C. 4

D. 5

E. 6



\(( \sqrt[3]{a} * \sqrt{b} )^6 = 500.........a^{\frac{6}{3}}*b^{\frac{6}{2}}=2^25^3.......a^2b^3=2^25^3\)...
so b = 5, and a = 2 or -2..
we rae looking for a+b, so two possibilities - 5+2=7 and 5-2=3

3 is in choices so B
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Re: If a and b are integers and (3a*b)^6 = 500, then a + b cou [#permalink]
I also thought it to be 7, But since its a could be question, we have to consider all possibilities. could be questions are tricky indeed.
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Re: If a and b are integers and (3a*b)^6 = 500, then a + b cou [#permalink]
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