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  • Typical Day of a UCLA MBA Student - Recording of Webinar with UCLA Adcom and Student

     December 14, 2018

     December 14, 2018

     10:00 PM PST

     11:00 PM PST

    Carolyn and Brett - nicely explained what is the typical day of a UCLA student. I am posting below recording of the webinar for those who could't attend this session.
  • Free GMAT Strategy Webinar

     December 15, 2018

     December 15, 2018

     07:00 AM PST

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    Aiming to score 760+? Attend this FREE session to learn how to Define your GMAT Strategy, Create your Study Plan and Master the Core Skills to excel on the GMAT.

A piece of cardboard measures 30 cm by 40 cm. We can make two differen

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Math Revolution GMAT Instructor
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A piece of cardboard measures 30 cm by 40 cm. We can make two differen  [#permalink]

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New post 23 Jul 2018, 00:17
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[Math Revolution GMAT math practice question]

A piece of cardboard measures 30 cm by 40 cm. We can make two different right circular cylinders by rolling the cardboard along its length and by rolling the cardboard along its width. What is the difference in their volumes?

\(A. \frac{1000}{π}\)
\(B. \frac{2000}{π}\)
\(C. \frac{3000}{π}\)
\(D. \frac{4000}{π}\)
\(E. \frac{5000}{π}\)

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Re: A piece of cardboard measures 30 cm by 40 cm. We can make two differen  [#permalink]

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New post 23 Jul 2018, 03:56
MathRevolution wrote:
[Math Revolution GMAT math practice question]

A piece of cardboard measures 30 cm by 40 cm. We can make two different right circular cylinders by rolling the cardboard along its length and by rolling the cardboard along its width. What is the difference in their volumes?

\(A. \frac{1000}{π}\)
\(B. \frac{2000}{π}\)
\(C. \frac{3000}{π}\)
\(D. \frac{4000}{π}\)
\(E. \frac{5000}{π}\)


If the cylinder is rolled along 30...
Circumference of circle so formed = 2πr=30.....r=15/π
Height =40
\(V=π*\frac{15}{π}^2*40\)

For the other volume 30 and 40 will interchange
So \(V=π*\frac{20}{π}^2*30\)....

Difference = \(\frac{20^2*30-15^2*40}{π}=(12000-9000)/π=3000/π\)

C
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Math Revolution GMAT Instructor
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Re: A piece of cardboard measures 30 cm by 40 cm. We can make two differen  [#permalink]

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New post 25 Jul 2018, 00:10
=>

Attachment:
7.23.png
7.23.png [ 4.04 KiB | Viewed 216 times ]


Case \(1: 2πr = 30\) and \(h = 40\)
\(r = \frac{15}{π}\)
The volume is \(πr^2*h = π(\frac{15}{π})^2 * 40 = \frac{( 225 * 40 )}{π} = \frac{9000}{π}.\)

Case 2: \(2πr = 40\) and \(h = 30\)
\(r = \frac{20}{π}\)
The volume is \(πr^2*h = π(\frac{20}{π})^2 * 30 = \frac{( 400 * 30 )}{π} = \frac{12000}{π}.\)

Thus, the difference in the two volumes is \(\frac{12000}{π} - \frac{9000}{π} = \frac{3000}{π}.\)


Therefore, C is the answer.
Answer: C
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Re: A piece of cardboard measures 30 cm by 40 cm. We can make two differen &nbs [#permalink] 25 Jul 2018, 00:10
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