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St1:
y(3y+7) = x
3y+7 = x/y
Since 3y + 7 must be integer, then x/y must be integer and x must be a multiple of y if x/y = integer.

St2:
x(x-1) = ym
(x/y)(x-1) = m
Since m is an integer, (x-1) is an integer then x/y must be an integer for the relationship to hold. So x must be a multiple of y.

St1: y(3y+7) = x 3y+7 = x/y Since 3y + 7 must be integer, then x/y must be integer and x must be a multiple of y if x/y = integer.

St2: x(x-1) = ym (x/y)(x-1) = m Since m is an integer, (x-1) is an integer then x/y must be an integer for the relationship to hold. So x must be a multiple of y.

Ans D

I do not think statement 2 can be sufficient. (x-1) and not x may be a multiple of y.

St1: y(3y+7) = x 3y+7 = x/y Since 3y + 7 must be integer, then x/y must be integer and x must be a multiple of y if x/y = integer.

St2: x(x-1) = ym (x/y)(x-1) = m Since m is an integer, (x-1) is an integer then x/y must be an integer for the relationship to hold. So x must be a multiple of y.

Ans D

I do not think statement 2 can be sufficient. (x-1) and not x may be a multiple of y.

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.

OK lets see...

x/y=N where N is an integer?

1) Y(3Y+7)=x; x/y= (3Y+7) we are told x and y are integers...therefor RHS is an integer...which inturn means RHS is an integer...therefore X is a multiple..sufficient..

2) x(x-1)=y/N ...we dont know if X or X-1 is the multiple of Y..therefore insufficient...

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

A too...........

from 1: 3y^2 + 7y = x
y (3y + 7) = x
in this case, 3y+7 is an integer. so x is a multiple of x.

from 2: x^2 - x = yk
x (x -1) = yk
x (x -1) = yk
k could be or could not be x or x-1. suppose, x = 4, x-1=3, k =1 and y = 12. in this case x is not a multiple of y. if x = 4, x-1 = 3, y = 3 and k =4, x is a multiple of y.

gmatclubot

Re: DS - number properties
[#permalink]
25 Jul 2007, 08:57