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GRE Math Challenge #73-If the cube of n is 180
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03 May 2015, 01:26
03 May 2015, 01:26
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Question Stats:
88% (01:42) correct
11% (02:34) wrong based on 26 sessions
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If the cube of n is 180 greater than the square of n, then n =
(A) 10
(B) 9
(C) 8
(D) 7
(E) 6
(A) 10
(B) 9
(C) 8
(D) 7
(E) 6
Re: GRE Math Challenge #73-If the cube of n is 180
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01 Jun 2016, 07:33
01 Jun 2016, 07:33
1
n^3-n^2=n^2(n-1)=n*n*n-1 = 180 the only way 180 can be written that way is 5*6*6 , Hence n = 6
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Re: GRE Math Challenge #73-If the cube of n is 180
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01 Jun 2016, 14:59
01 Jun 2016, 14:59
1
sandy wrote:
If the cube of n is 180 greater than the square of n, then n =
(A) 10
(B) 9
(C) 8
(D) 7
(E) 6
(A) 10
(B) 9
(C) 8
(D) 7
(E) 6
We get: n³ = n² + 180
Rearrange to get: n³ - n² = 180
Factor to get: n²(n - 1) = 180
Or... (n)(n)(n - 1) = 180
Test the answer choices to get....
n = 6
Show: ::
E
Cheers,
Brent
