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# AMOUNT OF BACTERIA PRESENT Time Amount 1:00 P.M. 10.0 grams

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Senior Manager
Joined: 02 Dec 2007
Posts: 448
AMOUNT OF BACTERIA PRESENT Time Amount 1:00 P.M. 10.0 grams [#permalink]

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08 Sep 2008, 04:47
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AMOUNT OF BACTERIA PRESENT
Time Amount
1:00 P.M. 10.0 grams
4:00 P.M. x grams
7:00 P.M. 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 P.M.?

A. 12.0
B. 12.1
C. 12.2
D. 12.3
E. 12.4

guys can anyone provide a short approach to this one without using quadratic equations or plugging answers ?
Intern
Joined: 19 Aug 2008
Posts: 1

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08 Sep 2008, 06:12
Let the amount of increase from 1-4pm and 4-7pm be y.

The equations can be written as
10+y=x - (1)
x+y=14.4 - (2)

Solving the 2 equations we get x=12.2

SVP
Joined: 29 Aug 2007
Posts: 2467

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08 Sep 2008, 07:32
Nihit wrote:
AMOUNT OF BACTERIA PRESENT
Time Amount
1:00 P.M. 10.0 grams
4:00 P.M. x grams
7:00 P.M. 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 P.M.?

A. 12.0
B. 12.1
C. 12.2
D. 12.3
E. 12.4

guys can anyone provide a short approach to this one without using quadratic equations or plugging answers ? thanks in advance

x/10 = 14.4/x
x = 12

A.
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SVP
Joined: 07 Nov 2007
Posts: 1789
Location: New York

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08 Sep 2008, 07:46
Nihit wrote:
AMOUNT OF BACTERIA PRESENT
Time Amount
1:00 P.M. 10.0 grams
4:00 P.M. x grams
7:00 P.M. 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 P.M.?

A. 12.0
B. 12.1
C. 12.2
D. 12.3
E. 12.4

guys can anyone provide a short approach to this one without using quadratic equations or plugging answers ?

(x-10)/10 =(14.4-x)/x
x*x=144
x=12
A
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Senior Manager
Joined: 04 Jan 2006
Posts: 276

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08 Sep 2008, 07:50
Nihit wrote:
AMOUNT OF BACTERIA PRESENT
Time Amount
1:00 P.M. 10.0 grams
4:00 P.M. x grams
7:00 P.M. 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 P.M.?

A. 12.0
B. 12.1
C. 12.2
D. 12.3
E. 12.4

guys can anyone provide a short approach to this one without using quadratic equations or plugging answers ?

My approach is the same as that above me.

(Time,Amount)
(0,10)
(3, 10x)
(6,10x^2)

Since
10(x^2) = 14.4
100(x^2) = 144 ---------- x 10
x^2 = 144/100
|x| = 12/10 ---------- sqrt
x = +1.2, -1.2

x can only be positive. Therefore, the amount of bacteria at 4:00PM = 10*1.2 = 12

A
SVP
Joined: 17 Jun 2008
Posts: 1529

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09 Sep 2008, 10:14
What is the OA?

Does "increase by same fraction" mean the ratio? To me, this means the difference and not the fraction and with this logic, x - 10 = 14.4 - x => x = 12.2

Am I interpreting something wrong here?
Manager
Joined: 03 Jun 2008
Posts: 135
Schools: ISB, Tuck, Michigan (Ross), Darden, MBS

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09 Sep 2008, 10:21
Nihit wrote:
AMOUNT OF BACTERIA PRESENT
Time Amount
1:00 P.M. 10.0 grams
4:00 P.M. x grams
7:00 P.M. 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 P.M.?

A. 12.0
B. 12.1
C. 12.2
D. 12.3
E. 12.4

guys can anyone provide a short approach to this one without using quadratic equations or plugging answers ?

The best way to solve this should be thru options.

Taking first option: 12

So from 10 to 12.. the percentage increase is 20 percent.

Similarly, from 12 to 14.4 the percentage increase is 20 percent.

SInce its the same percentage increase in both the cases, A has to be the answer.
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Re: short approach   [#permalink] 09 Sep 2008, 10:21
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# AMOUNT OF BACTERIA PRESENT Time Amount 1:00 P.M. 10.0 grams

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