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# When a certain projector is 3 feet from the screen the area

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When a certain projector is 3 feet from the screen the area [#permalink]  04 Feb 2008, 19:53
When a certain projector is 3 feet from the screen the area of the picture on the screen is 6 square feet. If the projector is moved to a position n times as far away from the screen, then the picture will take up n square times as much space on the screen. When this projector is 5 feet from the screen , the area, in square feet, of the picture on the screen is

1. 50/3
2. 24
3. 100/3
4. 36
5. 60
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Re: certain projector [#permalink]  04 Feb 2008, 20:59
(\frac{5}{3})^2 * 6 = \frac{50}{3}
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Re: certain projector [#permalink]  04 Feb 2008, 21:03
neelesh wrote:
(\frac{5}{3})^2 * 6 = \frac{50}{3}

can u explain it more clearly.
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Re: certain projector [#permalink]  04 Feb 2008, 21:07
since project is moved n times farther away it will take n-squared times area. Moving from 3 to 5 is like moving it by 5/3 times...hence (5/3)^2 of the original 6.
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Re: certain projector [#permalink]  04 Feb 2008, 21:20
5 is bigger than 3 5/3 times.

we are told that the size of the area increases by n^2, so the area increases by (5/3)^2 = 25/9

now, the final area will be (25/9)*6 = 50/3
Re: certain projector   [#permalink] 04 Feb 2008, 21:20
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