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# The number of organisms in a liter of water is approximately 6*10^23.

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The number of organisms in a liter of water is approximately 6*10^23.  [#permalink]

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11 Feb 2019, 01:13
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5% (low)

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83% (00:54) correct 17% (01:25) wrong based on 53 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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Re: The number of organisms in a liter of water is approximately 6*10^23.  [#permalink]

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11 Feb 2019, 07:00
Organisms in 1 liter = $$6*10^{23}$$
Organisms in 1/200 liter = x.

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

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Re: The number of organisms in a liter of water is approximately 6*10^23.  [#permalink]

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11 Feb 2019, 07:05
Bunuel wrote:
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) $$1.2*10^{26}$$

1 liter = $$6*10^{23}$$, number of organisms
1/200 liter = $$3*10^{21}$$

B
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Re: The number of organisms in a liter of water is approximately 6*10^23.  [#permalink]

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12 Feb 2019, 20:37
Bunuel wrote:
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) $$1.2*10^{26}$$

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.

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The number of organisms in a liter of water is approximately 6*10^23.  [#permalink]

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Updated on: 13 Feb 2019, 20:00
Bunuel wrote:
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!

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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Re: The number of organisms in a liter of water is approximately 6*10^23.  [#permalink]

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13 Feb 2019, 19:59
multiply both the number to get the answer

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Re: The number of organisms in a liter of water is approximately 6*10^23.  [#permalink]

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15 Feb 2019, 06:34
1 lit = $$6*10^{23}$$
1/200 lit = $$\frac{6*10^{23}}{200}$$ = $$3*10^{21}$$

Option B is correct
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Re: The number of organisms in a liter of water is approximately 6*10^23.  [#permalink]

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15 Feb 2019, 18:08
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jfranciscocuencag wrote:
Bunuel wrote:
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!

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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# Scott Woodbury-Stewart

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Re: The number of organisms in a liter of water is approximately 6*10^23.   [#permalink] 15 Feb 2019, 18:08
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