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OG PS 81 - Need help

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by srivats_nps » Sun Jul 17, 2011 10:12 am
Consider below info to be a table:
AMOUNT OF BACTERIA
TIME - AMOUNT
1PM - 10gms
4PM - x gms
7PM - 14.4 gms

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

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

* Can someone explain what is wrong with C ?
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by MBA.Aspirant » Sun Jul 17, 2011 10:33 am
x-10/10 = 14.4-x/x

x^2 =144

x =12

it increases by a factor of 0.2, so it was 10, it becomes 10 + 0.2*10= 12 * 1.2 = 14.4

if it was 12.2

then the factor is 12.2-10/10 = 0.22

then the end result would be 12.2 * 1.22 = 14.88
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by srivats_nps » Sun Jul 17, 2011 11:21 am
Ya...I get it ! I made a mistake by adding the common factor - 10 + 2.2=12.2 and then 12.2 + 2.2 = 14.4

So thought 2.2 would be the common factor and hence 12.2 :(
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by goalevan » Sun Jul 17, 2011 2:20 pm
x = ?

10(k) = x, where k is the unknown constant factor.

10(k)^2 = 144/10
k^2 = (144/100)
k = 12/10 = 1.2

10k = x = 12
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by dodgeforgmat » Sun Jul 17, 2011 10:30 pm
srivats_nps wrote:Consider below info to be a table:
AMOUNT OF BACTERIA
TIME - AMOUNT
1PM - 10gms
4PM - x gms
7PM - 14.4 gms

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

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

* Can someone explain what is wrong with C ?
You considered the values to be in Arithmetic Progression as opposed to Geometric Progression. Common factor is GP while Common difference is AP or HP
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