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Data for a certain biology experiment are given in the table

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Data for a certain biology experiment are given in the table [#permalink]

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New post 20 Aug 2011, 04:35
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Question Stats:

60% (01:07) correct 40% (00:49) wrong based on 80 sessions

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AMOUT OF BACTERIA PRESENT

Time Amount
1:00 pm 10.0 grams
4.00 pm x grams
7.00 pm 14.4 grams

Data for a certain biology experiment are given in the table above. If the amount of bacteria present increased by the same fraction during each of the two 3-hour periods shown, how many grams of bacteria were present at 4:00 pm?

a) 12.0
b) 12.1
c) 12.2
d) 12.3
e) 12.4
[Reveal] Spoiler: OA

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Re: a GWD math (7) , which hasn't been discussed [#permalink]

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New post 20 Aug 2011, 08:05
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Ratio problem

According to the given conditions

x/10=14.4/x
x^2=144
x=12
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Re: a GWD math (7) , which hasn't been discussed [#permalink]

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New post 20 Aug 2011, 10:11
let p be the fraction by which it increased

1pm 10 gms

4pm x gms = (1+p)10

7pm 14.4 gms = (1+p)x

=> x/10 = 14.4/x

=> x =12

Answer is A.

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Re: a GWD math (7) , which hasn't been discussed [#permalink]

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New post 21 Aug 2011, 01:30
Should the statement say something like "if the growth (or rate of growth) increases". Because if the amount increases by the same fraction, it would always double for example.

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Data for a certain biology experiment are given in the table [#permalink]

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New post 07 Nov 2017, 12:51
Jasontuyj2012 wrote:
AMOUT OF BACTERIA PRESENT

Time Amount
1:00 pm 10.0 grams
4.00 pm x grams
7.00 pm 14.4 grams

Data for a certain biology experiment are given in the table above. If the amount of bacteria present increased by the same fraction during each of the two 3-hour periods shown, how many grams of bacteria were present at 4:00 pm?

a) 12.0
b) 12.1
c) 12.2
d) 12.3
e) 12.4

Method I - Algebra - Multiplier

"The amount of bacteria present increased by the same fraction," \(x\), twice:
\((x*x) = x^2\) = the multiplier, twice

\(10 * x^2 = 14.4\)
\(x^2 = \frac{14.4}{10}\)
\(x = \sqrt{1.44}= 1.2 =\) the multiplier

Number of bacteria at 4 p.m.?

\(10 * 1.2 = 12\) bacteria present at 4 p.m.
(And \(12 * 1.2 = 14.4\) at 7 p.m. Correct.)

Answer A

Method II - Use answer choices

Start with (C) 12.2

Find one fractional increase:
\(\frac{12.2}{10} = 1.22\)

Result for the second fractional increase:
\(12 * 1.22 = 14.64\)

C's 4 p.m. value is too great. Eliminate D and E, which will be even greater.

Try A, the round number: 12

Fractional increase: \(\frac{12}{10} = 1.2\)
Multiply 4 p.m. value, 12, by 1.2:
\(12 * 1.2 = 14.4\). Correct.

Answer A

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Re: Data for a certain biology experiment are given in the table [#permalink]

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New post 12 Nov 2017, 07:22
Jasontuyj2012 wrote:
AMOUT OF BACTERIA PRESENT

Time Amount
1:00 pm 10.0 grams
4.00 pm x grams
7.00 pm 14.4 grams

Data for a certain biology experiment are given in the table above. If the amount of bacteria present increased by the same fraction during each of the two 3-hour periods shown, how many grams of bacteria were present at 4:00 pm?

a) 12.0
b) 12.1
c) 12.2
d) 12.3
e) 12.4


We can let n = the multiplier for each 3-hour period. So, we have:

1 p.m. = 10 grams

4 p.m. = 10n

7 p.m. = 10n^2

We can create the following equation:

10n^2 = 14.4

n^2 = 1.44

n = 1.2

Thus, we have 10n = 10(1.2) = 12 grams of bacteria at 4 p.m.

Alternate Solution:

Since the fractional increase is the same for both 3-hour periods, we must have:

x/10 = 14.4/x

x^2 = 144

x = 12 or x = -12

Since the number of bacteria cannot be negative, the answer is 12.

Answer: A
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Head of GMAT Instruction

GMAT Quant Self-Study Course
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Re: Data for a certain biology experiment are given in the table   [#permalink] 12 Nov 2017, 07:22
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