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bacteria

by dikku07 » Wed Sep 23, 2009 8:14 am
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


my answer isn't matching OA and I really don't get the explanation of OA. OA will come later
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by sreak1089 » Wed Sep 23, 2009 9:07 am
Is it C (12.2)?
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by ssmiles08 » Wed Sep 23, 2009 9:22 am
let f be the fraction increased during each of the 3 hour period.

10*f = x

x*f = 14.4 or f = 14.4/x

we want to find x.

10*(14.4/x) = x

144/x = x

x^2 = 144

x = +12 or -12. (-12 is invalid b/c there can not be negative grams)

x = 12 grams. IMO A.
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by mp2437 » Wed Sep 23, 2009 9:27 am
Agree with ssmiles08. "A" should be right answer.
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by dikku07 » Thu Sep 24, 2009 6:20 am
OA is A

I just tried 10+2.2=12.2
12.2+2.2=14.4

but i'm still wondering since increasing it by fraction 2.2, it matches the increase. but say, if the rate is 2 than how come it will be 12+2 will lead to 14.4 (if formula is not used)
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