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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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82% (00:55) correct 18% (01:17) wrong based on 67 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
1
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

Founder and CEO

Scott@TargetTestPrep.com
122 Reviews

5-star rated online GMAT quant
self study course

See why Target Test Prep is the top rated GMAT quant course on GMAT Club. Read Our Reviews

If you find one of my posts helpful, please take a moment to click on the "Kudos" button.

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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