Quasi Cylinder Question?

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ELYAC Realty: Senior | Next Rank: 100 Posts; Posts: 30; Joined: Sat Aug 30, 2008 12:23 am; Location: Los Angeles CA

by ELYAC Realty » Sat Aug 30, 2008 12:50 am

Why is pie used if ultimately this is a rectangle? Unless they want us to treat it as a cylinder? Any help would be great.

Thanks

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Source: Beat The GMAT — Problem Solving | Sat Aug 30, 2008 12:50 am

Stuart@KaplanGMAT: GMAT Instructor; Posts: 3225; Joined: Tue Jan 08, 2008 2:40 pmFollowed by: 614 members; Location: Toronto; Thanked: 1710 times; GMAT Score:800

Re: Quasi Cylinder Question?

by Stuart@KaplanGMAT » Sat Aug 30, 2008 2:01 am

ELYAC Realty wrote:Why is pie used if ultimately this is a rectangle? Unless they want us to treat it as a cylinder? Any help would be great.

Thanks

Because everyone loves pie!

Well, ok, because this isn't a rectangle.

The belt is wrapped around two semi-circles, so the length of the belt is 2 (length "L" between centres of circles) + 2(circumference of semi-circle).

We know that the diameter of each circle is 1, so the circumference of a full circle (which is the same as 2*(circumference of each semicircle)) is pi.

Therefore, we can come up with the equation:

2L + pi = 15
2L = 15 - pi
L = (15 - pi)/2

Stuart Kovinsky | Kaplan GMAT Faculty | Toronto

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ELYAC Realty: Senior | Next Rank: 100 Posts; Posts: 30; Joined: Sat Aug 30, 2008 12:23 am; Location: Los Angeles CA

by ELYAC Realty » Sat Aug 30, 2008 2:10 am

Thanks for your reply.

When you drawn a vertical line through both circles, doesn't that make it a rectangular?
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something like this, just imagine the lines are all straight. Is that all they want to know?

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Stuart@KaplanGMAT: GMAT Instructor; Posts: 3225; Joined: Tue Jan 08, 2008 2:40 pmFollowed by: 614 members; Location: Toronto; Thanked: 1710 times; GMAT Score:800

by Stuart@KaplanGMAT » Sat Aug 30, 2008 7:56 am

ELYAC Realty wrote:Thanks for your reply.

When you drawn a vertical line through both circles, doesn't that make it a rectangular?
_______
| |
|______|

something like this, just imagine the lines are all straight. Is that all they want to know?

You could draw a rectangle, but since the belt goes around the circles, not through them, the rectangle is irrelevant to the question.

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ELYAC Realty: Senior | Next Rank: 100 Posts; Posts: 30; Joined: Sat Aug 30, 2008 12:23 am; Location: Los Angeles CA

by ELYAC Realty » Sat Aug 30, 2008 9:09 am

I guess my confussion was with the questions. Bc my understanding was that they want the distance from one point to the next, which turns out to be the length of "L", but then you wold have to subtract the circumference of 2 half circles or one full circle. Got it. Thanks!

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