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Math Revolution GMAT Instructor V
Joined: 16 Aug 2015
Posts: 7465
GMAT 1: 760 Q51 V42 GPA: 3.82
For a,b,d are the positive integers, and d|a means that “a is divisibl  [#permalink]

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Difficulty:   25% (medium)

Question Stats: 76% (01:30) correct 24% (01:39) wrong based on 96 sessions

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For a,b,d are the positive integers, and d|a means that “a is divisible by d”, if d|ab, which of the following must be true?

A. d|a
B. d|b
C. d|2ab
D. d|(a+b)
E. d|(a-b)

* A solution will be posted in two days.

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Re: For a,b,d are the positive integers, and d|a means that “a is divisibl  [#permalink]

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d/a means a is divisible by d

d/ab means ab divisible by d.

all are integers so ,

if ab is divisible by d,

1 a can be divisible by d
or
2 b can be divisble by d.

so the question stem asks must true.

so option a and b are could but not must.

option c is 2ab divisible by d. if ab is divisible by d then 2ab is divisible by d.
option d and e we can't predict.

so option C is correct.
Math Revolution GMAT Instructor V
Joined: 16 Aug 2015
Posts: 7465
GMAT 1: 760 Q51 V42 GPA: 3.82
Re: For a,b,d are the positive integers, and d|a means that “a is divisibl  [#permalink]

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For a,b,d are the positive integers, and d|a means that “a is divisible by d”, if d|ab, which of the following must be true?

A. d|a
B. d|b
C. d|2ab
D. d|(a+b)
E. d|(a-b)

--> d|ab is ab=dk(k=integer) and also 2ab=2dk can be divided by d.
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Schools: AGSM '18
Re: For a,b,d are the positive integers, and d|a means that “a is divisibl  [#permalink]

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HI MathRevolution,

MathRevolution wrote:
For a,b,d are the positive integers, and d|a means that “a is divisible by d”, if d|ab, which of the following must be true?

A. d|a
B. d|b
C. d|2ab
D. d|(a+b)
E. d|(a-b)

--> d|ab is ab=dk(k=integer) and also 2ab=2dk can be divided by d.

d/ab = k => dk = ab. I dont know how could you give conclusion that ab= dk?
Math Revolution GMAT Instructor V
Joined: 16 Aug 2015
Posts: 7465
GMAT 1: 760 Q51 V42 GPA: 3.82
Re: For a,b,d are the positive integers, and d|a means that “a is divisibl  [#permalink]

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oanhnguyen1116 wrote:
HI MathRevolution,

MathRevolution wrote:
For a,b,d are the positive integers, and d|a means that “a is divisible by d”, if d|ab, which of the following must be true?

A. d|a
B. d|b
C. d|2ab
D. d|(a+b)
E. d|(a-b)

--> d|ab is ab=dk(k=integer) and also 2ab=2dk can be divided by d.

d/ab = k => dk = ab. I dont know how could you give conclusion that ab= dk?

-> Because ab is divisible by d.
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Intern  Joined: 07 Jan 2016
Posts: 23
Schools: AGSM '18
Re: For a,b,d are the positive integers, and d|a means that “a is divisibl  [#permalink]

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Thank you MathRevolution Current Student D
Joined: 12 Aug 2015
Posts: 2610
Schools: Boston U '20 (M)
GRE 1: Q169 V154 Re: For a,b,d are the positive integers, and d|a means that “a is divisibl  [#permalink]

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Nice question..
Here as AB/D = integer hence 2AB/D = integer
Hence C
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Re: For a,b,d are the positive integers, and d|a means that “a is divisibl  [#permalink]

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_________________ Re: For a,b,d are the positive integers, and d|a means that “a is divisibl   [#permalink] 26 Dec 2018, 11:17
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