collection of tough problems from G PREP - 42

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by sanju09 » Mon Feb 08, 2010 3:49 am
abhasjha wrote:If x and y are integers greater than 1, is x a multiple of y?

(1) 3y^2+7y=x

(2) X^2-X is a multiple of y.
(1) with y (3 y + 7) = x, x surely is a multiple of y. Sufficient

(2) with x (x - 1) = k y, we can never be sure that x is a multiple of y. Insufficient

[spoiler]A[/spoiler]
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by ajith » Tue Feb 09, 2010 3:36 am
abhasjha wrote:If x and y are integers greater than 1, is x a multiple of y?

(1) 3y^2+7y=x

(2) X^2-X is a multiple of y.
(1) (3y+7)*y = x

say y=kx

(3kx+7)*kx = x
(3k+7)*k = 1

only possible if 3k+1 = k =1 which is not possible

Sufficient


2)y = k * (x-1)*x

Sufficient to conclude that x is a multiple of y
[spoiler]

D[/spoiler]
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by sanju09 » Tue Feb 09, 2010 3:43 am
ajith wrote:
abhasjha wrote:If x and y are integers greater than 1, is x a multiple of y?

(1) 3y^2+7y=x

(2) X^2-X is a multiple of y.
(1) (3y+7)*y = x

say y=kx

(3kx+7)*kx = x
(3k+7)*k = 1

only possible if 3k+1 = k =1 which is not possible

Sufficient


2)y = k * (x-1)*x

Sufficient to conclude that x is a multiple of y
[spoiler]

D[/spoiler]
What's the difference in a factor and a multiple?
The mind is everything. What you think you become. -Lord Buddha



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by ajith » Tue Feb 09, 2010 4:25 am
sanju09 wrote: What's the difference in a factor and a multiple?
Oops a mistake in my answer - Thanks Sanju
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