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For a light that has an intensity of 60 candles at its sourc
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13 Feb 2014, 01:17
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The Official Guide For GMAT® Quantitative Review, 2ND EditionFor a light that has an intensity of 60 candles at its source, the intensity in candles, S, of the light at a point d feet from the source is given by the formula \(S=\frac{60k}{d^2}\), where k is a constant. If the intensity of the light is 30 candles at a distance of 2 feet from the source, what is the intensity of the light at a distance of 20 feet from the source? (A) 3/10 candles (B) 1/2 candles (C) 1 1/3 candles (D) 2 candles (E) 3 candles Problem Solving Question: 91 Category: Algebra Applied problems Page: 73 Difficulty: 600 GMAT Club is introducing a new project: The Official Guide For GMAT® Quantitative Review, 2ND Edition  Quantitative Questions ProjectEach week we'll be posting several questions from The Official Guide For GMAT® Quantitative Review, 2ND Edition and then after couple of days we'll provide Official Answer (OA) to them along with a slution. We'll be glad if you participate in development of this project: 1. Please provide your solutions to the questions; 2. Please vote for the best solutions by pressing Kudos button; 3. Please vote for the questions themselves by pressing Kudos button; 4. Please share your views on difficulty level of the questions, so that we have most precise evaluation. Thank you!
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Re: For a light that has an intensity of 60 candles at its sourc
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13 Feb 2014, 01:17
SOLUTIONFor a light that has an intensity of 60 candles at its source, the intensity in candles, S, of the light at a point d feet from the source is given by the formula S=60k/d^2, where k is a constant. If the intensity of the light is 30 candles at a distance of 2 feet from the source, what is the intensity of the light at a distance of 20 feet from the source?(A) 3/10 candles (B) 1/2 candles (C) 1 1/3 candles (D) 2 candles (E) 3 candles The intensity of the light is 30 candles (S) at a distance of 2 feet (d) from the source: \(30=\frac{60k}{2^2}\) > \(k=2\). Therefore the intensity of the light at a distance of 20 feet from the source is \(S=\frac{60*2}{20^2}=\frac{3}{10}\). Answer: A.
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Re: For a light that has an intensity of 60 candles at its sourc
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13 Feb 2014, 10:30
For a light that has an intensity of 60 candles at its source, the intensity in candles, S, of the light at a point d feet from the source is given by the formula S=60k/d^2, where k is a constant. If the intensity of the light is 30 candles at a distance of 2 feet from the source, what is the intensity of the light at a distance of 20 feet from the source? Sol: For the given intensity S=30 candles at a distance of 2 feet we can find value of k as 30*d^2/60= k 30*4/60 so k=2 Now substituting the value of k and d=20 ft we get S= 60*2/(20^2) Or 120/400 = 3/10 candles Ans A Posted from my mobile device
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Re: For a light that has an intensity of 60 candles at its sourc
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13 Feb 2014, 21:38
For a light that has an intensity of 60 candles at its source, the intensity in candles, S, of the light at a point d feet from the source is given by the formula \(S=\frac{60k}{d^2}\), where k is a constant. If the intensity of the light is 30 candles at a distance of 2 feet from the source, what is the intensity of the light at a distance of 20 feet from the source?
(A) 3/10 candles (B) 1/2 candles (C) 1 1/3 candles (D) 2 candles (E) 3 candles
Using the formula \(S=\frac{60k}{d^2}\), the ratio between light intensity at 2 feet and 20 feet \(=\frac{Light Intensity At 20 Feet}{Light Intensity At 2 Feet}=\frac{60k}{20^2}/\frac{60k}{2^2}= \frac{1}{100}\) Given that light intensity at 2 feet equals 30 candles, the intensity of light at 20 feet is equal to \(30(\frac{1}{100}) = \frac{3}{10} candles\)
Answer: (A)



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Re: For a light that has an intensity of 60 candles at its sourc
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15 Feb 2014, 09:55
Bunuel wrote: The Official Guide For GMAT® Quantitative Review, 2ND EditionFor a light that has an intensity of 60 candles at its source, the intensity in candles, S, of the light at a point d feet from the source is given by the formula S=60k/d^2, where k is a constant. If the intensity of the light is 30 candles at a distance of 2 feet from the source, what is the intensity of the light at a distance of 20 feet from the source? (A) 3/10 candles (B) 1/2 candles (C) 1 1/3 candles (D) 2 candles (E) 3 candles 30 = 60* k/4 => k =2 60*2/20*20 = 3/10  Option A)
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Re: For a light that has an intensity of 60 candles at its sourc
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16 Feb 2014, 01:41
option A. First we can calculate the value of k by putting S=30 and d=2 in S=60k/d^2 From this k=2 Now we can calculate S=60*2/(20)^2 S=3/10



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Re: For a light that has an intensity of 60 candles at its sourc
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16 Feb 2014, 23:56
SOLUTIONFor a light that has an intensity of 60 candles at its source, the intensity in candles, S, of the light at a point d feet from the source is given by the formula S=60k/d^2, where k is a constant. If the intensity of the light is 30 candles at a distance of 2 feet from the source, what is the intensity of the light at a distance of 20 feet from the source?(A) 3/10 candles (B) 1/2 candles (C) 1 1/3 candles (D) 2 candles (E) 3 candles The intensity of the light is 30 candles (S) at a distance of 2 feet (d) from the source: \(30=\frac{60k}{2^2}\) > \(k=2\). Therefore the intensity of the light at a distance of 20 feet from the source is \(S=\frac{60*2}{20^2}=\frac{3}{10}\). Answer: A.
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Re: For a light that has an intensity of 60 candles at its sourc
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30 Dec 2016, 16:18
Bunuel wrote: SOLUTION
For a light that has an intensity of 60 candles at its source, the intensity in candles, S, of the light at a point d feet from the source is given by the formula S=60k/d^2, where k is a constant. If the intensity of the light is 30 candles at a distance of 2 feet from the source, what is the intensity of the light at a distance of 20 feet from the source?
(A) 3/10 candles (B) 1/2 candles (C) 1 1/3 candles (D) 2 candles (E) 3 candles
The intensity of the light is 30 candles (S) at a distance of 2 feet (d) from the source: \(30=\frac{60k}{2^2}\) > \(k=2\).
Therefore the intensity of the light at a distance of 20 feet from the source is \(S=\frac{60*2}{20^2}=\frac{3}{10}\).
Answer: A. Hi, Bunuel. I chose C because I think candle can not be apart, that means the number of candle is integer. Why the number of candle can be fraction? Thanks in advance:) It changed in the OG Quantitive 2017 where the choices are A) 3/10 candle B) 1/2 candle C) 1 candle D) 2 candles E) 3 candles. And the question remains the same.



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Re: For a light that has an intensity of 60 candles at its sourc
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31 Dec 2016, 01:42
Jez0612 wrote: Bunuel wrote: SOLUTION
For a light that has an intensity of 60 candles at its source, the intensity in candles, S, of the light at a point d feet from the source is given by the formula S=60k/d^2, where k is a constant. If the intensity of the light is 30 candles at a distance of 2 feet from the source, what is the intensity of the light at a distance of 20 feet from the source?
(A) 3/10 candles (B) 1/2 candles (C) 1 1/3 candles (D) 2 candles (E) 3 candles
The intensity of the light is 30 candles (S) at a distance of 2 feet (d) from the source: \(30=\frac{60k}{2^2}\) > \(k=2\).
Therefore the intensity of the light at a distance of 20 feet from the source is \(S=\frac{60*2}{20^2}=\frac{3}{10}\).
Answer: A. Hi, Bunuel. I chose C because I think candle can not be apart, that means the number of candle is integer. Why the number of candle can be fraction? Thanks in advance:) It changed in the OG Quantitive 2017 where the choices are A) 3/10 candle B) 1/2 candle C) 1 candle D) 2 candles E) 3 candles. And the question remains the same. Intensity is kind of a unit of a brightness, so it's not actual candles, so we can have an intensity in fractions.
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Re: For a light that has an intensity of 60 candles at its sourc
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31 Dec 2016, 02:39
60k/2^2 = 30 => k=2
So if d=20 then 60*2/20*20 == 3/10



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For a light that has an intensity of 60 candles at its source
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31 May 2017, 18:10
rlevochkin wrote: For a light that has an intensity of 60 candles at its source, the intensity in candles, S, of the light at a point d d feet from the source is given by the formula S=60k/d^2 60, where k is a constant. If the intensity of the light is 30 candles at a distance of 2 feet from the source, what is the intensity of the light at a distance of 20 feet from the source?
A. 3/10 candles B. 1/2 candles C. 1 1/3 candles D. 2 candles E. 3 candles We are given that for a light that has an intensity of 60 candles at its source, the intensity in candles, S, of the light at a point d feet from the source is given by the formula S=60k/d^2, where k is a constant. For this direct variation problem, we first will use the given formula to solve for k, the constant of variation, and then we can answer the question. 30 = 60k/(2^2) 30 = 60k/4 120 = 60k k = 2 We know that k is 2, and we use that fact to determine the intensity of the light at a distance of 20 feet from the source. S = 60(2)/20^2 S = 120/400 = 12/40 = 3/10 candles Answer: A
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Re: For a light that has an intensity of 60 candles at its sourc
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12 Oct 2018, 02:53
WoundedTiger wrote: For a light that has an intensity of 60 candles at its source, the intensity in candles, S, of the light at a point d feet from the source is given by the formula S=60k/d^2, where k is a constant. If the intensity of the light is 30 candles at a distance of 2 feet from the source, what is the intensity of the light at a distance of 20 feet from the source?
Sol: For the given intensity S=30 candles at a distance of 2 feet we can find value of k as
30*d^2/60= k 30*4/60 so k=2
Now substituting the value of k and d=20 ft we get S= 60*2/(20^2) Or 120/400 = 3/10 candles
Ans A
Posted from my mobile device HI ! Can someone please explain why Ks coeffficient ( 60 ) remains the same . Thats what threw me !




Re: For a light that has an intensity of 60 candles at its sourc
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