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# Consider the formula H = 2a^3/b. If a is doubled and b is increased

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Math Expert
Joined: 02 Sep 2009
Posts: 52906
Consider the formula H = 2a^3/b. If a is doubled and b is increased  [#permalink]

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03 Dec 2015, 05:30
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Difficulty:

15% (low)

Question Stats:

72% (01:04) correct 28% (02:10) wrong based on 124 sessions

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Consider the formula $$H = \frac{2a^3}{b}$$. If a is doubled and b is increased by a factor of 4, by what factor is H increased?

A. 2
B. 4
C. 6
D. 8
E. 16

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Joined: 20 Feb 2015
Posts: 795
Concentration: Strategy, General Management
Re: Consider the formula H = 2a^3/b. If a is doubled and b is increased  [#permalink]

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03 Dec 2015, 05:43
after applying ----------- stated in question

H' = 2*(2a)^3/4b
H' = 2*8a^3/4b
H' = 8/4(H)
H' = 2 H
Thus A
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Re: Consider the formula H = 2a^3/b. If a is doubled and b is increased  [#permalink]

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03 Dec 2015, 06:29
H = (2a^3)/b
if a is doubled and b is incresead by factor of 4 then equation becomes
H = [2*(2a)^3] / 4b
H = 16a^3 / 4b
H = 4a^3 / b

Initially H = (2a^3) / b, Now H = (4a^3) / b which means H has been increased by a factor of 2.

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Joined: 09 Sep 2015
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Re: Consider the formula H = 2a^3/b. If a is doubled and b is increased  [#permalink]

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03 Dec 2015, 07:01
A..

h= 2 (8) A^3/(4) B

HENCE A
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Re: Consider the formula H = 2a^3/b. If a is doubled and b is increased  [#permalink]

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06 Sep 2018, 17:18
The question formation is wrong, when we are saying that "b" is increased by a factor of 4 ,this means that my new b will be b+4k form. If the question formed was b is increased to a factor of 4 then b will be 4k. If the answer to the question has to be A.2 then b must be written simply become 4 times.
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Re: Consider the formula H = 2a^3/b. If a is doubled and b is increased  [#permalink]

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07 Sep 2018, 05:31
I agree I also interpreted the question as b+4b...I would like to know what is wrong with my thinking...thanks.

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Re: Consider the formula H = 2a^3/b. If a is doubled and b is increased  [#permalink]

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08 Sep 2018, 03:58
Bunuel wrote:
Consider the formula $$H = \frac{2a^3}{b}$$. If a is doubled and b is increased by a factor of 4, by what factor is H increased?

A. 2
B. 4
C. 6
D. 8
E. 16

Hi Bunel, b is increased by factor k means bk + k or bk ?

was stuck by this for some time
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Re: Consider the formula H = 2a^3/b. If a is doubled and b is increased  [#permalink]

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09 Sep 2018, 02:19
H=$$\frac{2a^3}{b}$$ --> H= $$\frac{a^3}{b}$$*2

The increase results in the following equation:

$$\frac{2*(2a)^3}{4b}$$ --> $$\frac{16a^3}{4b}$$ --> $$\frac{4a^3}{b}$$ --> $$\frac{a^3}{b}$$*4
2*2=4 Hence, A.
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Re: Consider the formula H = 2a^3/b. If a is doubled and b is increased   [#permalink] 09 Sep 2018, 02:19
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