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# If b= , a is halved, and c is doubled, by what percentage wi

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GMAT Club Legend
Joined: 07 Jun 2014
Posts: 4750
GRE 1: Q167 V156
WE: Business Development (Energy and Utilities)
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Kudos [?]: 1662 [1] , given: 396

If b= , a is halved, and c is doubled, by what percentage wi [#permalink]  29 Jan 2018, 15:16
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Question Stats:

57% (00:52) correct 42% (02:06) wrong based on 14 sessions
If $$b=\frac{4a}{c}$$ , a is halved, and c is doubled, by what percentage will b decrease?
A. 4%
B. 25%
C. 50%
D. 75%
E. 100%

Drill 1
Question: 14
Page: 495
[Reveal] Spoiler: OA

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Sandy
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Director
Joined: 20 Apr 2016
Posts: 758
Followers: 6

Kudos [?]: 514 [0], given: 94

Re: If b= , a is halved, and c is doubled, by what percentage wi [#permalink]  30 Jan 2018, 07:58
sandy wrote:
If $$b=\frac{4a}{c}$$ , a is halved, and c is doubled, by what percentage will b decrease?
A. 4%
B. 25%
C. 50%
D. 75%
E. 100%

Here let take a=10 , c= 2 (for easy calculation we want to keep the value of b as integer and not fraction)

so b =$$\frac{(4 * 10)}{(2)}$$

or b= 20

Now a is halved = $$\frac{10}{2}$$ = 5

and c is doubled = 2+2 = 4

Now b= $$\frac{(4 * 5)}{(4)}$$ = 5

Therefore percentage decrease = $$\frac{(5-20)}{20}* 100$$ = -75% i.e decrease
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Intern
Joined: 07 Oct 2017
Posts: 30
Followers: 1

Kudos [?]: 4 [0], given: 0

Re: If b= , a is halved, and c is doubled, by what percentage wi [#permalink]  03 Feb 2018, 04:01
Thank you.
GMAT Club Legend
Joined: 07 Jun 2014
Posts: 4750
GRE 1: Q167 V156
WE: Business Development (Energy and Utilities)
Followers: 93

Kudos [?]: 1662 [0], given: 396

Re: If b= , a is halved, and c is doubled, by what percentage wi [#permalink]  04 Mar 2018, 14:24
Expert's post
Explanation

Try plugging in values for a and c. Let a = 6 and c = 2.

Then b= =3. If a is halved, equal it will 3. If c is doubled, it will equal 4. So now, b= =3.

Because the question is looking for a percentage decrease, apply the percentage change formula:

$$\frac{12-3}{12}\times 100=\frac{9}{12}\times 100=75%$$.
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Sandy
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Re: If b= , a is halved, and c is doubled, by what percentage wi   [#permalink] 04 Mar 2018, 14:24
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