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Re: DS - Water evaporates at the rate of two liters (m07q26) [#permalink]

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08 Jun 2013, 08:19

Rocky423 wrote:

Its not required for the answers to be same. The question is, what is sufficient to solve the problem. In this case it can be solved by either of the option.

The statements are always True. Its a common mistake by people to try to verify a Statement. This also serves as a great rule to catch the errors that is the statements never contradict each other. True, they wont always be sufficient, but they will never be mutually exclusive.

Hence, if you think that two statements are not agreeing with each other its time to recheck the work as you have most probably made an error.
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Re: DS - Water evaporates at the rate of two liters (m07q26) [#permalink]

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11 Jun 2013, 08:09

I answer B because aside from St2, the question and St1 dont indicate whether is a rectangle prism pool or a cylinder pool. As far as I know I cannot use information from St2 (cylinder pool) to answer the question with St1.

On the other hand, Bunnuels revised version is better since the question itself is saying that the pool is right circular cylinder. IMO, this is a poor constructed question.

What am I missing here?
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Re: DS - Water evaporates at the rate of two liters (m07q26) [#permalink]

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13 Jun 2013, 22:43

marcovg4 wrote:

I answer B because aside from St2, the question and St1 dont indicate whether is a rectangle prism pool or a cylinder pool. As far as I know I cannot use information from St2 (cylinder pool) to answer the question with St1.

On the other hand, Bunnuels revised version is better since the question itself is saying that the pool is right circular cylinder. IMO, this is a poor constructed question.

What am I missing here?

Hi marcovg4, Pay attention to the fact that we have been given volume in the Question stem. Volume by its basic definition is equal to the area of the surface * Height

In the first statment we have not been told that its a rectangular prism or cylinder pool, But does it matter? If its rectangular den it would be (l*b) * h = 56 Therefore, the surface area = (pie * r *r) *h = 56

However, yeah the values probably do not agree with each other as the answer from 1st statement looks like an approximate from 2nd statement. So yeah, that is poorly constructed, However i still do not see why the shape should be an issue here since the question already says that is has vertical walls and a flat bottom.
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Re: DS - Water evaporates at the rate of two liters (m07q26) [#permalink]

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26 Dec 2013, 17:46

The part that is throwing me off in the revised version of the question is "Water evaporates at the rate of two liters per hour per one square meter of surface"

What does this exactly mean? and why would we just consider the top surface alone and not total surface area?

My understanding was we would need both 'r' and 'h' since Total surface area of cylinder = \(2\pi * r(r+h)\) = say x If water evaporates 2 liters per hour per one sq. meter, therefore for x, the rate must be 2x.

Therefore time taken for 30 lit = 30/2x (where x = \(2\pi * r(r+h)\))

No?

Bunuel wrote:

xALIx wrote:

Water evaporates at the rate of two liters per hour per one square meter of surface. How long will it take to evaporate 30 liters of water from a swimming pool full of water with vertical walls and a flat bottom that holds 56 cubic meters of water?

1. The depth of the pool is 2 meters 2. The pool is circular with a radius of 3 meters

A right circular cylinder of 72 cubic meters is completely filled with water. If water evaporates from the cylinder at a constant rate of two liters per hour per one square meter of surface, how long will it take for 30 liters of water to evaporate?

To find the time needed for 30 liters of water to evaporate we need to find the surface area of the top of the cylinder: \(\frac{area}{2}\) will be the amount of water that evaporates each hour, thus \(time=\frac{30}{(\frac{area}{2})}\).

On the other hand since \(volume=\pi{r^2}h=72\) then \(area=\pi{r^2}=\frac{72}{h}\). So, basically all we need is ether the area of the surface or the height of the cylinder.

(1) The height of the cylinder is 2 meters. Sufficient. (2) The radius of the base of the cylinder is \(\frac{6}{\sqrt{\pi}}\) meters --> \(area=\pi{r^2}=36\). Sufficient.

The part that is throwing me off in the revised version of the question is "Water evaporates at the rate of two liters per hour per one square meter of surface"

What does this exactly mean? and why would we just consider the top surface alone and not total surface area?

Bunuel wrote:

xALIx wrote:

Water evaporates at the rate of two liters per hour per one square meter of surface. How long will it take to evaporate 30 liters of water from a swimming pool full of water with vertical walls and a flat bottom that holds 56 cubic meters of water?

1. The depth of the pool is 2 meters 2. The pool is circular with a radius of 3 meters

A right circular cylinder of 72 cubic meters is completely filled with water. If water evaporates from the cylinder at a constant rate of two liters per hour per one square meter of surface, how long will it take for 30 liters of water to evaporate?

To find the time needed for 30 liters of water to evaporate we need to find the surface area of the top of the cylinder: \(\frac{area}{2}\) will be the amount of water that evaporates each hour, thus \(time=\frac{30}{(\frac{area}{2})}\).

On the other hand since \(volume=\pi{r^2}h=72\) then \(area=\pi{r^2}=\frac{72}{h}\). So, basically all we need is ether the area of the surface or the height of the cylinder.

(1) The height of the cylinder is 2 meters. Sufficient. (2) The radius of the base of the cylinder is \(\frac{6}{\sqrt{\pi}}\) meters --> \(area=\pi{r^2}=36\). Sufficient.

Answer: D.

Water evaporates from the top of a pool, which is open. We are told that 2 liters evaporate from each square meter of surface per 1 hour.
_________________

Re: DS - Water evaporates at the rate of two liters (m07q26) [#permalink]

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27 Dec 2013, 18:06

I think I get it now. Thanks!

Looks like we are using terms "pool" and "cylinder" quite interchangeably between the old and the new version of the question which is causing some confusion. My vote will be to reword the newer version of the question if possible..

"If water evaporates from the top surface of the cylinder at a constant rate of two liters per hour per one square meter of surface, how long will it take for 30 liters of water to evaporate?"

Re: DS - Water evaporates at the rate of two liters (m07q26) [#permalink]

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27 May 2014, 01:29

Hi,

Water evaporates at the rate of two liters per hour per one square meter of surface. How long will it take to evaporate 30 liters of water from a swimming pool full of water with vertical walls and a flat bottom that holds 56 cubic meters of water?

1. The depth of the pool is 2 meters 2. The pool is circular with a radius of 3 meters

----- The Goal of the above problem is to determine the surface area of the swimming pool...

1. If u know the height of the pool the area will be = volume/height = 56/2 - Sufficient 2. u can determine the surface area by the formula (Pie).(radius)^2 = (3.14)(3)^2 - Sufficient

Re: DS - Water evaporates at the rate of two liters (m07q26) [#permalink]

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27 May 2014, 05:55

Bunuel wrote:

xALIx wrote:

Water evaporates at the rate of two liters per hour per one square meter of surface. How long will it take to evaporate 30 liters of water from a swimming pool full of water with vertical walls and a flat bottom that holds 56 cubic meters of water?

1. The depth of the pool is 2 meters 2. The pool is circular with a radius of 3 meters

A right circular cylinder of 72 cubic meters is completely filled with water. If water evaporates from the cylinder at a constant rate of two liters per hour per one square meter of surface, how long will it take for 30 liters of water to evaporate?

To find the time needed for 30 liters of water to evaporate we need to find the surface area of the top of the cylinder: \(\frac{area}{2}\) will be the amount of water that evaporates each hour, thus \(time=\frac{30}{(\frac{area}{2})}\).

On the other hand since \(volume=\pi{r^2}h=72\) then \(area=\pi{r^2}=\frac{72}{h}\). So, basically all we need is ether the area of the surface or the height of the cylinder.

(1) The height of the cylinder is 2 meters. Sufficient. (2) The radius of the base of the cylinder is \(\frac{6}{\sqrt{\pi}}\) meters --> \(area=\pi{r^2}=36\). Sufficient.

Answer: D.

Hi Bunuel,

How did u get the radius of the base of the cylinder as \(\frac{6}{\sqrt{\pi}}\) meters for statement 2. Did u use the height given in the first statement?
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Water evaporates at the rate of two liters per hour per one square meter of surface. How long will it take to evaporate 30 liters of water from a swimming pool full of water with vertical walls and a flat bottom that holds 56 cubic meters of water?

1. The depth of the pool is 2 meters 2. The pool is circular with a radius of 3 meters

A right circular cylinder of 72 cubic meters is completely filled with water. If water evaporates from the cylinder at a constant rate of two liters per hour per one square meter of surface, how long will it take for 30 liters of water to evaporate?

To find the time needed for 30 liters of water to evaporate we need to find the surface area of the top of the cylinder: \(\frac{area}{2}\) will be the amount of water that evaporates each hour, thus \(time=\frac{30}{(\frac{area}{2})}\).

On the other hand since \(volume=\pi{r^2}h=72\) then \(area=\pi{r^2}=\frac{72}{h}\). So, basically all we need is ether the area of the surface or the height of the cylinder.

(1) The height of the cylinder is 2 meters. Sufficient. (2) The radius of the base of the cylinder is \(\frac{6}{\sqrt{\pi}}\) meters --> \(area=\pi{r^2}=36\). Sufficient.

Answer: D.

Hi Bunuel,

How did u get the radius of the base of the cylinder as \(\frac{6}{\sqrt{\pi}}\) meters for statement 2. Did u use the height given in the first statement?

It's directly given there. See the revised version of this question is as follow:

A right circular cylinder of 72 cubic meters is completely filled with water. If water evaporates from the cylinder at a constant rate of two liters per hour per one square meter of surface, how long will it take for 30 liters of water to evaporate?

(1) The height of the cylinder is 2 meters. (2) The radius of the base of the cylinder is \(\frac{6}{\sqrt{\pi}}\) meters.
_________________