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Dillesh4096
Bunuel
A right cylinder and a cube have the same surface area. If the height of the cylinder is equal to its diameter, then the volume of the cylinder is approximately what percent greater than the volume of the cube?

A. 6%
B. 13%
C. 26%
D. 32%
E. 35%

Given, h = 2r
Let r = 1, h = 2

Surface area of cylinder = 2πr(h + r)
= 2πr(2r + r) = 6π

Surface area of cube = 6a^2

A right cylinder and a cube have the same surface area
—> 6π = 6a^2
—> a^2 = π
—> a = √π

% greater = (volume of cylinder - volume of cube)/volume of cube*100
= (πr^2h - a^3)/a^3*100
= (2π - π√π)/π√π*100
= (2/√π - 1)*100
= (2/√3.14 - 1)*100
= 13%


Posted from my mobile device

is there any simple way to calculate the last step here?
i.e 2/√\(\pi\) - 1 = 0.13 ??

This seems too tedious and difficult to solve.

Please help
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DarkHorse2019
is there any simple way to calculate the last step here?
i.e 2/√\(\pi\) - 1 = 0.13 ??

This seems too tedious and difficult to solve.

Please help

Hi DarkHorse2019,

So √3.14 is close to 1.8 [ Since 18^2 = 3.24]

Now, let’s see value of 2/1.8 - 1 = 0.2/1.8 = 2/18 = 1/9 in fraction
In % = 1/9*100 = 100/9 = (11-12)%

So, 13% after assumptions

Also note that other options are quite distant.

Hope it helps!

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Dillesh4096
Bunuel
A right cylinder and a cube have the same surface area. If the height of the cylinder is equal to its diameter, then the volume of the cylinder is approximately what percent greater than the volume of the cube?

A. 6%
B. 13%
C. 26%
D. 32%
E. 35%

Given, h = 2r
Let r = 1, h = 2

Surface area of cylinder = 2πr(h + r)
= 2πr(2r + r) = 6π

Surface area of cube = 6a^2

A right cylinder and a cube have the same surface area
—> 6π = 6a^2
—> a^2 = π
—> a = √π

% greater = (volume of cylinder - volume of cube)/volume of cube*100
= (πr^2h - a^3)/a^3*100
= (2π - π√π)/π√π*100
= (2/√π - 1)*100
= (2/√3.14 - 1)*100
= 13%

IMO Option B

Pls Hit kudos if you like the solution

Posted from my mobile device

For questions like this where the actual values aren't given for the dimensions, I have two questions.

1. How do we know when it is appropriate to use sample values?
2. How should we think about what appropriate values we can use? e.g. What are valid values?
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