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A thin piece of wire 40 meters long is cut into two pieces.

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Director
Joined: 05 Feb 2006
Posts: 893

Kudos [?]: 131 [1], given: 0

A thin piece of wire 40 meters long is cut into two pieces. [#permalink]

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28 Oct 2006, 02:25
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Difficulty:

45% (medium)

Question Stats:

66% (01:38) correct 34% (01:25) wrong based on 175 sessions

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A thin piece of wire 40 meters long is cut into two pieces. One piece is used to form a circle with radius r, and the other is used to form a square. No wire is left over. Which of the following represents the total area, in square meters, of the circular and the square regions in terms of r?

A. $$\pi*r^2$$
B. $$\pi*r^2 + 10$$
C. $$\pi*r^2 + \frac{1}{4}*\pi^2*r^2$$
D. $$\pi*r^2 + (40 - 2\pi*r)^2$$
E. $$\pi*r^2 + (10 - \frac{1}{2}\pi*r)^2$$

OPEN DISCUSSION OF THIS QUESTION IS HERE: a-thin-piece-of-paper-40-mt-long-106671.html
[Reveal] Spoiler: OA

Kudos [?]: 131 [1], given: 0

Math Expert
Joined: 02 Sep 2009
Posts: 42630

Kudos [?]: 135806 [2], given: 12714

Re: A thin piece of wire 40 meters long is cut into two pieces. [#permalink]

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28 Nov 2012, 02:20
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nelz007 wrote:
Is there any other way to solve this question?

A thin piece of wire 40 meters long is cut into two pieces. One piece is used to form a circle with radius r, and the other is used to form a square. No wire is left over. Which of the following represents the total area, in square meters, of the circular and the square regions in terms of r?

A. $$\pi*r^2$$
B. $$\pi*r^2 + 10$$
C. $$\pi*r^2 + \frac{1}{4}*\pi^2*r^2$$
D. $$\pi*r^2 + (40 - 2\pi*r)^2$$
E. $$\pi*r^2 + (10 - \frac{1}{2}\pi*r)^2$$

The area of a circle will be - $$\pi{r^2}$$ and $$2\pi{r}$$ meters of wire will be used;
There will be $$40-2\pi{r}$$ meters of wire left for a square. Side of this square will be $$\frac{40-2\pi{r}}{4}=10-\frac{\pi{r}}{2}$$, hence the area of the square will be $$(10-\frac{\pi{r}}{2})^2$$.

The total area will be - $$\pi{r^2}+(10-\frac{\pi{r}}{2})^2$$.

OPEN DISCUSSION OF THIS QUESTION IS HERE: a-thin-piece-of-paper-40-mt-long-106671.html
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Kudos [?]: 135806 [2], given: 12714

Senior Manager
Joined: 30 Aug 2006
Posts: 373

Kudos [?]: 75 [0], given: 0

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28 Oct 2006, 02:54
E

((40 - 2pir)/4)^2 + pir^2

(10 - 1/2pir) ^2 + pir^2

Kudos [?]: 75 [0], given: 0

Manager
Joined: 21 Sep 2012
Posts: 234

Kudos [?]: 417 [0], given: 63

Re: A thin piece of wire 40 meters long is cut into two pieces. [#permalink]

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28 Nov 2012, 00:41
Is there any other way to solve this question?

Kudos [?]: 417 [0], given: 63

Re: A thin piece of wire 40 meters long is cut into two pieces.   [#permalink] 28 Nov 2012, 00:41
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