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This is a "what is the value of..." DS question. In this type of question, a statement will be sufficient only if it leads to a single value of the variable (or expression) you're asked about.

Remember, surface area of a cylinder = 2 π r² + 2 π r h where r is the radius of the cylinder, h is its height and π is a constant. The ratio between the surface areas of the two cylinders can be determined either by calculating the two surface areas or by identifying relationships between r and h of the two.

Stat. (1) + (2) Combined, you get the relationship between the radii as well as heights of the two cylinders. Let 2r be the radius of cylinder A and r be the radius of cylinder B as per Stat. (1), and let h be the height of both cylinders as the height of cylinder A is equal to that of cylinder B. By plugging in these in the formula of the surface area of a cylinder, you find that the surface area of cylinder A = 8 π r² + 4 π r h and that of cylinder B = 2 π r² + 2π r h. It is not possible to determine the ratio between the surface areas of cylinder A and B without knowing the specific values of r and h.

Stat.(1) + (2)->IS->E.

So I understand the math and was able to get to the point of cylinder A = 8 π r² + 4 π r h and that of cylinder B = 2 π r² + 2π r h.

But the provided solution only says that "It is not possible to determine the ratio between the surface areas of cylinder A and B without knowing the specific values of r and h."

I don't understand why. I chose C because we're given the relationship between the two diameters, in addition to H.

This is a "what is the value of..." DS question. In this type of question, a statement will be sufficient only if it leads to a single value of the variable (or expression) you're asked about.

Remember, surface area of a cylinder = 2 π r² + 2 π r h where r is the radius of the cylinder, h is its height and π is a constant. The ratio between the surface areas of the two cylinders can be determined either by calculating the two surface areas or by identifying relationships between r and h of the two.

Stat. (1) + (2) Combined, you get the relationship between the radii as well as heights of the two cylinders. Let 2r be the radius of cylinder A and r be the radius of cylinder B as per Stat. (1), and let h be the height of both cylinders as the height of cylinder A is equal to that of cylinder B. By plugging in these in the formula of the surface area of a cylinder, you find that the surface area of cylinder A = 8 π r² + 4 π r h and that of cylinder B = 2 π r² + 2π r h. It is not possible to determine the ratio between the surface areas of cylinder A and B without knowing the specific values of r and h.

Stat.(1) + (2)->IS->E.

So I understand the math and was able to get to the point of cylinder A = 8 π r² + 4 π r h and that of cylinder B = 2 π r² + 2π r h.

But the provided solution only says that "It is not possible to determine the ratio between the surface areas of cylinder A and B without knowing the specific values of r and h."

I don't understand why. I chose C because we're given the relationship between the two diameters, in addition to H.

So to know the ratio, we need atleast r in terms of h. What makes a hemisphere,cylinder, cone, and cuboid different from a sphere and square is the presence of a "+" in the calculation of the total surface area.

While the given data would have been sufficient had the cylinders been open at the top and bottom, it is not sufficient in the case of normal cylinders.

Kudos Please... If my post helped.
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Re: The surface area of cylinder A is how many times the surface [#permalink]

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30 May 2015, 04:22

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Remember, surface area of a cylinder = 2 π r² + 2 π r h where r is the radius of the cylinder, h is its height and π is a constant. The ratio between the surface areas of the two cylinders can be determined either by calculating the two surface areas or by identifying relationships between r and h of the two.

Stat. (1) + (2) Combined, you get the relationship between the radii as well as heights of the two cylinders. Let 2r be the radius of cylinder A and r be the radius of cylinder B as per Stat. (1), and let h be the height of both cylinders as the height of cylinder A is equal to that of cylinder B. By plugging in these in the formula of the surface area of a cylinder, you find that the surface area of cylinder A = 8 π r² + 4 π r h and that of cylinder B = 2 π r² + 2π r h. It is not possible to determine the ratio between the surface areas of cylinder A and B without knowing the specific values of r and h.

Stat.(1) + (2)->IS->E.

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Re: The surface area of cylinder A is how many times the surface [#permalink]

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09 Jul 2016, 13:33

Hello from the GMAT Club BumpBot!

Thanks to another GMAT Club member, I have just discovered this valuable topic, yet it had no discussion for over a year. I am now bumping it up - doing my job. I think you may find it valuable (esp those replies with Kudos).

Want to see all other topics I dig out? Follow me (click follow button on profile). You will receive a summary of all topics I bump in your profile area as well as via email.
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Re: The surface area of cylinder A is how many times the surface [#permalink]

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13 Jul 2016, 21:13

Wording of Question is ambiguous... It is not clear if it is asking total surface area or just lateral/ curved surface area...could someone clarify ???

Wording of Question is ambiguous... It is not clear if it is asking total surface area or just lateral/ curved surface area...could someone clarify ???

Posted from my mobile device

It's total area. If it were otherwise it would have been explicitly mentioned.
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Re: The surface area of cylinder A is how many times the surface [#permalink]

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14 Jul 2016, 17:07

1

This post received KUDOS

If you find this question on the real GMAT, you should first be very wary because each statement alone is quite obviously insufficient. Even if you didn't know the surface area formula, it should be clear looking at each statement that you need both pieces of info. This is a very clear C trap question and I think the best bet would be to just try plugging in easy numbers to see both statements fall short.

Make the height equal to 1 Try radius 2 for bigger cylinder, radius 1 for smaller, then try radius 4 for bigger, 2 for smaller. Quick calculations and it becomes clear answer is E

Re: The surface area of cylinder A is how many times the surface [#permalink]

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18 Jul 2016, 13:57

LXVE wrote:

If you find this question on the real GMAT, you should first be very wary because each statement alone is quite obviously insufficient. Even if you didn't know the surface area formula, it should be clear looking at each statement that you need both pieces of info. This is a very clear C trap question and I think the best bet would be to just try plugging in easy numbers to see both statements fall short.

Make the height equal to 1 Try radius 2 for bigger cylinder, radius 1 for smaller, then try radius 4 for bigger, 2 for smaller. Quick calculations and it becomes clear answer is E

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