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Sub 505 (Easy)|   Arithmetic|   Exponents|      
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Bunuel
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The number of organisms in a liter of water is approximately 6*10^23. 11 Feb 2019, 01:13
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86% (00:53) correct 14% (01:21) wrong based on 104 sessions

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The number of organisms in a liter of water is approximately \(6*10^{23}\). Assuming this number is correct, about how many organisms exist in a covered Petri dish that contains 1/200 liters of water?


(A) 6.9

(B) \(3*10^{21}\)

(C) \(6*10^{22}\)

(D) \(3*10^{23}\)

(E) \(1.2*10^{26}\)
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B
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The number of organisms in a liter of water is approximately 6*10^23. 11 Feb 2019, 07:00
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Organisms in 1 liter = \(6*10^{23}\)
Organisms in 1/200 liter = x.

x = \(\frac{6*10^{23}}{200}\) = \(3*10^{21}\)

B is the answer.
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The number of organisms in a liter of water is approximately 6*10^23. 11 Feb 2019, 07:05
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Bunuel
The number of organisms in a liter of water is approximately \(6*10^{23}\). Assuming this number is correct, about how many organisms exist in a covered Petri dish that contains 1/200 liters of water?


(A) 6.9

(B) \(3*10^{21}\)

(C) \(6*10^{22}\)

(D) \(3*10^{23}\)

(E) \(1.2*10^{26}\)
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1 liter = \(6*10^{23}\), number of organisms
1/200 liter = \(3*10^{21}\)

B
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The number of organisms in a liter of water is approximately 6*10^23. 12 Feb 2019, 20:37
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Bunuel
The number of organisms in a liter of water is approximately \(6*10^{23}\). Assuming this number is correct, about how many organisms exist in a covered Petri dish that contains 1/200 liters of water?


(A) 6.9

(B) \(3*10^{21}\)

(C) \(6*10^{22}\)

(D) \(3*10^{23}\)

(E) \(1.2*10^{26}\)
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We can create the proportion:

(6 x 10^23)/1 = n/(1/200)

6 x 10^23 = 200n

3 x 10^23 = 100n

(3 x 10^23)/100 = n

3 x 10^21 = n

Alternate Solution:

Let’s re-express 6 x 10^23 as 600 x 10^21 organisms in 1 liter. Since we have 1/200 of a liter in our Petri dish, we divide 600 x 10^21 by 200, giving us 3 x 10^21 organisms.

Answer: B
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The number of organisms in a liter of water is approximately 6*10^23. Updated on: 13 Feb 2019, 20:00
Originally posted by jfranciscocuencag on 13 Feb 2019, 19:53.
Last edited by jfranciscocuencag on 13 Feb 2019, 20:00, edited 1 time in total.
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Bunuel
The number of organisms in a liter of water is approximately \(6*10^{23}\). Assuming this number is correct, about how many organisms exist in a covered Petri dish that contains 1/200 liters of water?


(A) 6.9

(B) \(3*10^{21}\)

(C) \(6*10^{22}\)

(D) \(3*10^{23}\)

(E) \(1.2*10^{26}\)
Show more

Hello ScottTargetTestPrep !

I choosed the correct answer but a concept is still not really clear for me, if the question is telling us that the number of organisms in a liter of water is approximately \(6*10^{23}\) and is asking us to find how many organisms exist in 1/200 liters of water...

Why it does not mean the following?

\(((6*10^{23})/1)/(1/200)\)

Which actually will deliver us to the option E...

Thank you so much in advance!
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The number of organisms in a liter of water is approximately 6*10^23. 13 Feb 2019, 19:59
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answer must be B.
multiply both the number to get the answer

Posted from my mobile device
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The number of organisms in a liter of water is approximately 6*10^23. 15 Feb 2019, 06:34
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1 lit = \(6*10^{23}\)
1/200 lit = \(\frac{6*10^{23}}{200}\) = \(3*10^{21}\)

Option B is correct
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The number of organisms in a liter of water is approximately 6*10^23. 15 Feb 2019, 18:08
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jfranciscocuencag
Bunuel
The number of organisms in a liter of water is approximately \(6*10^{23}\). Assuming this number is correct, about how many organisms exist in a covered Petri dish that contains 1/200 liters of water?


(A) 6.9

(B) \(3*10^{21}\)

(C) \(6*10^{22}\)

(D) \(3*10^{23}\)

(E) \(1.2*10^{26}\)

Hello ScottTargetTestPrep !

I choosed the correct answer but a concept is still not really clear for me, if the question is telling us that the number of organisms in a liter of water is approximately \(6*10^{23}\) and is asking us to find how many organisms exist in 1/200 liters of water...

Why it does not mean the following?

\(((6*10^{23})/1)/(1/200)\)

Which actually will deliver us to the option E...

Thank you so much in advance!
Show more

We are given the number of organisms in one liter of water (6*10^23) and are asked to find the number of organisms in 1/200 liters of water. Suppose that we were asked to find the organisms in 200 liters of water instead; what would you do? You would naturally multiply the organisms per liter figure by the number of liters and answer as 6*(10^23)*(200). What we did in the question is essentially the same, the only difference is that we multiplied by 1/200 instead of 200.

Just as a note, if the question had given us the number of organisms in 1/200 liters of water and asked for the number of organisms in one liter of water, the answer would have been exactly what you suggested.
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