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If (1+x)y=y, which of the following must be true?

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Math Revolution GMAT Instructor
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If (1+x)y=y, which of the following must be true?  [#permalink]

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New post 01 Jul 2016, 02:27
00:00
A
B
C
D
E

Difficulty:

  35% (medium)

Question Stats:

63% (01:06) correct 37% (01:20) wrong based on 111 sessions

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If (1+x)y=y, which of the following must be true?
A. x=-1 or y=0
B. x=0 or y=0
C. x=1 or y=1
D. x=-1 or y=-1
E. x=0 or y=1

*An answer will be posted in 2 days.

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Re: If (1+x)y=y, which of the following must be true?  [#permalink]

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New post 01 Jul 2016, 04:15
We have (1+x)y=y.

If x=0, y=y. True
If y=0, (1+x)*0=0 True

So, B will be the answer.

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Re: If (1+x)y=y, which of the following must be true?  [#permalink]

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New post 03 Jul 2016, 17:26
From y+xy=y, we get xy=0. Hence, the correct answer is B.
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Re: If (1+x)y=y, which of the following must be true?  [#permalink]

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New post 03 Jul 2016, 21:21
MathRevolution wrote:
From y+xy=y, we get xy=0. Hence, the correct answer is B.


MathRevolution
By only having xy=0, we cannot say answer is B as A and E options also satisfy the condition xy=0.

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Re: If (1+x)y=y, which of the following must be true?  [#permalink]

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New post 18 Sep 2016, 04:09
(1+x)y = y
y +xy = y
y + xy - y = 0
xy = 0
so x= 0 or y = 0
correct answer - B
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Re: If (1+x)y=y, which of the following must be true?  [#permalink]

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New post 18 Sep 2016, 04:36
(1+x)Y=Y

since y is variable n we don`t know its sign hence cant eliminate directly.
so lets bring bring y to left side i.e. (1+x)y-y=0
here y is common i.e. Y(1+x-1)=0
by solving inner side of the bracket we got y(x) =0 & this is only possible when either of x or y must be zero
hence B is coorect
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If (1+x)y=y, which of the following must be true?  [#permalink]

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New post 24 Mar 2019, 18:48
Hello MathRevolution Bunuel !

Could someone explain to me the difference between B & E?

\((1 + x)y = y\)

\(1 + x = 1\)

\(x = 0\)

So y could be 0 or 1.

\((1 + 0)0 = 0\) ... true

\((1 + 0)1 = 1\) ... also true

Kind regards!
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If (1+x)y=y, which of the following must be true?   [#permalink] 24 Mar 2019, 18:48
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