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If |d-9| = 2d, then d=

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Director
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If |d-9| = 2d, then d=  [#permalink]

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18 Jan 2007, 07:49
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If |d - 9| = 2d, then d=

(A) -9
(B) -3
(C) 1
(D) 3
(E) 9
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Joined: 02 Sep 2009
Posts: 49271
If |d-9| = 2d, then d=  [#permalink]

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23 Jan 2011, 08:37
3
2
aurobindo wrote:
If |d-9| = 2d, then d=
(A) -9
(B) -3
(C) 1
(D) 3
(E) 9

You can approach this problem in several ways. For example: given |d-9| = 2d --> as LHS (|d-9|) is an absolute value then it's non-negative so RHS (2d or simply d) must also be non-negative thus answer choices A and B are out. Next you can quickly substitute the values to see that d=3 satisfies given inequality: |3-9|=|-6|=6=2*3.

Or you can try algebraic approach and expand |d-9| for 2 ranges:
If $$0\leq{d}\leq{9}$$ then $$-(d-9)=2d$$ --> $$d=3$$ --> you have an answer D right away;
Just to check the second range: If $${d}>9$$ then $$d-9=2d$$ --> $$d=-9$$ --> not a valid solution as $$d$$ cannot be negative (also this value is not in the range we are considering).

Hope it's clear.
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Re: PS: Modulus D  [#permalink]

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10 Sep 2009, 11:40
15
3
If |d-9| = 2d, then d=
(A) -9
(B) -3
(C) 1
(D) 3
(E) 9

now the two eqs are
1) when (d-9) > 0
d-9 = 2d
d = -9

2) when (d-9) < 0
9-d = 2d
d = 3

the two initial solns are d = -9 and 3

but when we substitute d = -9 in original equation we get
|-9-9| = 2 * -9
18 = -18
which is not possible

Hence only solution is d = 3.
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Re: PS: Modulus D  [#permalink]

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18 Jan 2007, 09:42
2
1
if d>9, on solving eqn u get d = -9 which is impossible since d>9.
if d<9, on sloving u get d = 3. Hence D is correct answer
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19 Jan 2007, 03:31
4
1
IMO

2d is an absolute value, so d can't be negative.

Out of the +ve nos. d can be only 3
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19 Jan 2007, 05:31
Sumithra wrote:
IMO

2d is an absolute value, so d can't be negative.

Out of the +ve nos. d can be only 3

Same approach : it's better to plug 2 values mentally with the respect of abs always positive (or 0) than to solve the original equation (saving energy... 4 hours is long)
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If |d-9| = 2d, then d=  [#permalink]

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15 Jan 2015, 08:25
I am having some problems with the range when there is an absolute value. Can I find some good material that explains how we get to the range?

Thank you,
Natalia
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Re: If |d-9| = 2d, then d=  [#permalink]

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15 Jan 2015, 22:47
Hi All,

Since the answer choices to this question are NUMBERS, we can use them (along with some Number Property knowledge) to quickly get to the solution by TESTing THE ANSWERS.

We're given |D - 9| = 2D and we're asked to solve for D

Since the "left" side of the equation will end up as either a 0 or a POSITIVE, the "right side" of the equation CAN'T be negative, so we know that D CANNOT be NEGATIVE.
Eliminate A and B.

The solution MUST be one of the remaining 3 answers, so we can just TEST them until we find the correct one.

Could D = 1?
|1-9| = |-8| = 8
2D = 2(1) = 2
-8 does NOT = 2
Eliminate C.

Could D = 3?
|3-9| = |-6| = 6
2(3) = 6
6 DOES = 6
This IS the answer.

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Re: If |d-9| = 2d, then d=  [#permalink]

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02 Mar 2015, 02:26
pacifist85 wrote:
I am having some problems with the range when there is an absolute value. Can I find some good material that explains how we get to the range?

Thank you,
Natalia

Hi Natalia! (Looks like you are Russian=))
I think you can read in Gmat Club Mathbook if you still need this information
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If |d-9| = 2d, then d=  [#permalink]

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07 May 2015, 23:33
1
Here's a more visual way to think through the given equation |d - 9| = 2d.

|d-9| represents the distance between point d and 9 on the number line. Now, there are only 2 options - either the point d can lie on the LEFT hand side of 9 (At a distance of |d-9| units from 9) or on the RIGHT hand side of 9.

So, let's depict these two cases on the number line.

Case 1: d < 9

In this case, |d - 9| = 9 - d (also written as -(d-9))

So, the given equation becomes:

9 - d = 2d
=> d = 3

Case 2: d > 9

In this case, |d - 9| = d - 9

So, the given equation becomes:

d - 9 = 2d
=> d = -9

But this value of d contradicts the condition of Case 2, that d is greater than 9. Therefore, this value of d can be rejected.

So, we get d = 3.

Usually, this visual way of thinking through absolute value expressions helps a lot in situations where you find yourself getting confused about how to open an absolute value expression, what signs to put, what cases to consider etc.

Hope this helped!

Japinder
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Re: If |d-9| = 2d, then d=  [#permalink]

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26 Aug 2016, 07:34
Top Contributor
aurobindo wrote:
If |d - 9| = 2d, then d=

(A) -9
(B) -3
(C) 1
(D) 3
(E) 9

We have two cases to consider:
d - 9 = 2d and d - 9 = -2d

case a: If d - 9 = 2d, then d = -9
When we check this solution for extraneous roots, we get: |-9 - 9| = (2)(-9)
Simplify to get: |-18| = -18
NO GOOD!
So, d = -9 is NOT a valid solution

case b: If d - 9 = -2d, then d = 3
When we check this solution for extraneous roots, we get: |3 - 9| = (2)(3)
Simplify to get: |-6| = 6
WORKS!
So, d = 3 IS a valid solution.

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Joined: 21 Jun 2017
Posts: 85
Re: If |d-9| = 2d, then d=  [#permalink]

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13 Oct 2017, 08:09
aurobindo wrote:
If |d - 9| = 2d, then d=

(A) -9
(B) -3
(C) 1
(D) 3
(E) 9

First, we know that D has to be a positive, because + x + is always a positive; and the absolute value is always positive. Eliminate A, B
Eliminate 1 because, 8 does not equal 2, eliminate 9 because 0 does not equal 18

Therefore (D) 3 is the answer
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Re: If |d-9| = 2d, then d=  [#permalink]

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27 Nov 2017, 19:10
aurobindo wrote:
If |d - 9| = 2d, then d=

(A) -9
(B) -3
(C) 1
(D) 3
(E) 9

We can solve the equation, first, when (d - 9) is positive, and second, when (d - 9) is negative.

When (d - 9) is positive:

d - 9 = 2d

-9 = d

Looking at the original equation, we see that if d = -9, then |d - 9| = |-18| = 18, but 2d = 2(-9) = -18. We see that is not possible.

So, let’s now solve the equation when (d - 9) is negative.

-(d - 9) = 2d

-d + 9 = 2d

9 = 3d

3 = d

We see that if d = 3, then |3 - 9| = |-6| = 6 and 2d = 2(3) = 6. Thus, d must be 3.

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Re: If |d-9| = 2d, then d= &nbs [#permalink] 27 Nov 2017, 19:10
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