Last visit was: 19 Nov 2025, 06:14 It is currently 19 Nov 2025, 06:14
Home
GMAT
Messages
Tests
Schools
Events
Rewards
Chat
My Profile
Close
GMAT Club Daily Prep
Thank you for using the timer - this advanced tool can estimate your performance and suggest more practice questions. We have subscribed you to Daily Prep Questions via email.

Customized
for You

we will pick new questions that match your level based on your Timer History

Track
Your Progress

every week, we’ll send you an estimated GMAT score based on your performance

Practice
Pays

we will pick new questions that match your level based on your Timer History
Not interested in getting valuable practice questions and articles delivered to your email? No problem, unsubscribe here.
Go to My Error Log Learn more
Close
Request Expert Reply
Confirm Cancel
Back to Forum
Create Topic
Sub 505 Level|   Word Problems|                           
User avatar
Bunuel
User avatar
Math Expert
Joined: 02 Sep 2009
Last visit: 19 Nov 2025
Posts: 105,388
Own Kudos:
778,221
 [45]
Given Kudos: 99,977
Products:
GMAT Club Tests Forum Quiz
Expert
Expert reply
Active GMAT Club Expert! Tag them with @ followed by their username for a faster response.
Posts: 105,388
Kudos: 778,221
 [45]
For a light that has an intensity of 60 candles at its source, the int 13 Feb 2014, 02:17
Kudos
Add Kudos
45
Bookmarks
Bookmark this Post
00:00
Start Timer
Pause Timer
Resume Timer
Show Answer
Hide
Show
History
A
Be sure to select an answer first to save it in the Error Log before revealing the correct answer (OA)!

Difficulty:

5% (low)

Question Stats:

88% (01:57) correct 12% (02:24) wrong based on 1274 sessions

History

Date
Time
Result
Not Attempted Yet
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
ShowHide Answer
Official Answer
A
Most Helpful Reply
User avatar
Bunuel
User avatar
Math Expert
Joined: 02 Sep 2009
Last visit: 19 Nov 2025
Posts: 105,388
Own Kudos:
778,221
 [13]
Given Kudos: 99,977
Products:
GMAT Club Tests Forum Quiz
Expert
Expert reply
Active GMAT Club Expert! Tag them with @ followed by their username for a faster response.
Posts: 105,388
Kudos: 778,221
 [13]
For a light that has an intensity of 60 candles at its source, the int 13 Feb 2014, 02:17
5
Kudos
Add Kudos
8
Bookmarks
Bookmark this Post
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.
General Discussion
User avatar
WoundedTiger
User avatar
Joined: 25 Apr 2012
Last visit: 25 Sep 2024
Posts: 521
Own Kudos:
2,534
 [1]
Given Kudos: 740
Location: India
GPA: 3.21
WE:Business Development (Other)
Products:
My Reviews
Posts: 521
Kudos: 2,534
 [1]
For a light that has an intensity of 60 candles at its source, the int 13 Feb 2014, 11:30
1
Kudos
Add Kudos
Bookmarks
Bookmark this Post
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
User avatar
arunspanda
User avatar
Joined: 04 Oct 2013
Last visit: 31 Oct 2021
Posts: 127
Own Kudos:
333
 [2]
Given Kudos: 55
Location: India
GMAT Date: 05-23-2015
GPA: 3.45
Products:
My Reviews
Posts: 127
Kudos: 333
 [2]
For a light that has an intensity of 60 candles at its source, the int 13 Feb 2014, 22:38
2
Kudos
Add Kudos
Bookmarks
Bookmark this Post
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)
User avatar
kinjiGC
User avatar
Joined: 03 Feb 2013
Last visit: 12 Oct 2025
Posts: 791
Own Kudos:
2,717
 [1]
Given Kudos: 567
Location: India
Concentration: Operations, Strategy
Schools: Tepper '17 (M$) W.P. Carey '17 (A$) NUS '17 (A)
GMAT 1: 760 Q49 V44
GPA: 3.88
WE:Engineering (Computer Software)
Products:
My Reviews
Schools: Tepper '17 (M$) W.P. Carey '17 (A$) NUS '17 (A)
GMAT 1: 760 Q49 V44
Posts: 791
Kudos: 2,717
 [1]
For a light that has an intensity of 60 candles at its source, the int 15 Feb 2014, 10:55
1
Kudos
Add Kudos
Bookmarks
Bookmark this Post
Bunuel
The Official Guide For GMAT® Quantitative Review, 2ND Edition

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

Show more

30 = 60* k/4 => k =2
60*2/20*20 = 3/10 - Option A)
avatar
AKG1593
avatar
Joined: 20 Dec 2013
Last visit: 30 Mar 2024
Posts: 182
Own Kudos:
324
Given Kudos: 35
Location: India
Posts: 182
Kudos: 324
For a light that has an intensity of 60 candles at its source, the int 16 Feb 2014, 02:41
Kudos
Add Kudos
Bookmarks
Bookmark this Post
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
avatar
Jez0612
avatar
Joined: 10 Dec 2016
Last visit: 24 Jul 2017
Posts: 2
Given Kudos: 8
Posts: 2
Kudos: 0
For a light that has an intensity of 60 candles at its source, the int 30 Dec 2016, 17:18
Kudos
Add Kudos
Bookmarks
Bookmark this Post
Bunuel
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.
Show more

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.
User avatar
Bunuel
User avatar
Math Expert
Joined: 02 Sep 2009
Last visit: 19 Nov 2025
Posts: 105,388
Own Kudos:
778,221
Given Kudos: 99,977
Products:
GMAT Club Tests Forum Quiz
Expert
Expert reply
Active GMAT Club Expert! Tag them with @ followed by their username for a faster response.
Posts: 105,388
Kudos: 778,221
For a light that has an intensity of 60 candles at its source, the int 31 Dec 2016, 02:42
Kudos
Add Kudos
Bookmarks
Bookmark this Post
Jez0612
Bunuel
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.
Show more

Intensity is kind of a unit of a brightness, so it's not actual candles, so we can have an intensity in fractions.
avatar
sai897
avatar
Joined: 01 Aug 2016
Last visit: 27 Aug 2017
Posts: 18
Own Kudos:
5
Given Kudos: 74
Schools: ISB '18
Schools: ISB '18
Posts: 18
Kudos: 5
For a light that has an intensity of 60 candles at its source, the int 31 Dec 2016, 03:39
Kudos
Add Kudos
Bookmarks
Bookmark this Post
60k/2^2 = 30 => k=2

So if d=20 then 60*2/20*20 == 3/10
User avatar
JeffTargetTestPrep
User avatar
Target Test Prep Representative
Joined: 04 Mar 2011
Last visit: 05 Jan 2024
Posts: 2,977
Own Kudos:
8,389
Given Kudos: 1,646
Status:Head GMAT Instructor
Affiliations: Target Test Prep
Expert
Expert reply
Posts: 2,977
Kudos: 8,389
For a light that has an intensity of 60 candles at its source, the int 31 May 2017, 19:10
Kudos
Add Kudos
Bookmarks
Bookmark this Post
rlevochkin
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
Show more

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
avatar
whelmedbynumbers
avatar
Joined: 25 Apr 2018
Last visit: 24 Oct 2018
Posts: 1
Given Kudos: 1
Posts: 1
Kudos: 0
For a light that has an intensity of 60 candles at its source, the int 12 Oct 2018, 03:53
Kudos
Add Kudos
Bookmarks
Bookmark this Post
WoundedTiger
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
Show more

HI !

Can someone please explain why Ks coeffficient ( 60 ) remains the same . Thats what threw me !
avatar
Hanzel101
avatar
Joined: 15 Jul 2016
Last visit: 23 Feb 2020
Posts: 72
Own Kudos:
92
Given Kudos: 190
Location: India
Schools: Oxford "21 (A) Cambridge "21 (A$)
GMAT 1: 690 Q48 V36
Schools: Oxford "21 (A) Cambridge "21 (A$)
GMAT 1: 690 Q48 V36
Posts: 72
Kudos: 92
For a light that has an intensity of 60 candles at its source, the int 10 Aug 2019, 23:02
Kudos
Add Kudos
Bookmarks
Bookmark this Post
whelmedbynumbers
WoundedTiger
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 !
Show more

I have the same question.

Bunuel egmat VeritasKarishma please help!
User avatar
Argp
User avatar
Joined: 10 Aug 2019
Last visit: 30 May 2022
Posts: 44
Own Kudos:
10
Given Kudos: 151
Location: India
Posts: 44
Kudos: 10
For a light that has an intensity of 60 candles at its source, the int 02 Jan 2021, 00:40
Kudos
Add Kudos
Bookmarks
Bookmark this Post
whelmedbynumbers
WoundedTiger
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 !
Show more

chetan2u Bunuel, I have the same question. Can you help clarify? Thank you!
User avatar
chetan2u
User avatar
GMAT Expert
Joined: 02 Aug 2009
Last visit: 15 Nov 2025
Posts: 11,238
Own Kudos:
43,702
 [1]
Given Kudos: 335
Status:Math and DI Expert
Location: India
Concentration: Human Resources, General Management
GMAT Focus 1: 735 Q90 V89 DI81
Products:
My Reviews
Expert
Expert reply
GMAT Focus 1: 735 Q90 V89 DI81
Posts: 11,238
Kudos: 43,702
 [1]
For a light that has an intensity of 60 candles at its source, the int 02 Jan 2021, 04:16
1
Kudos
Add Kudos
Bookmarks
Bookmark this Post
Argp
whelmedbynumbers
WoundedTiger
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 !

chetan2u Bunuel, I have the same question. Can you help clarify? Thank you!
Show more


Hi
The light is the same in all 3 calculations and has an intensity of 60 candles at the source. It decreases as we move away from light, so d, the distance, in the formula changes.
Rest everything remains the same.

Maybe if we were dealing with some other light that has an intensity of 30 candles AT THE SOURCE, the 60 would have changed but then too, it would be mention that 60 is the luminosity related to candles at the source.
User avatar
bumpbot
User avatar
Non-Human User
Joined: 09 Sep 2013
Last visit: 04 Jan 2021
Posts: 38,586
Own Kudos:
1,079
Posts: 38,586
Kudos: 1,079
For a light that has an intensity of 60 candles at its source, the int 25 Sep 2025, 14:20
Kudos
Add Kudos
Bookmarks
Bookmark this Post
Hello from the GMAT Club BumpBot!

Thanks to another GMAT Club member, I have just discovered this valuable topic, yet it had no discussion for over a year. I am now bumping it up - doing my job. I think you may find it valuable (esp those replies with Kudos).

Want to see all other topics I dig out? Follow me (click follow button on profile). You will receive a summary of all topics I bump in your profile area as well as via email.
Moderators:
Bunuel
Math Expert
105388 posts
Krunaal
Tuck School Moderator
805 posts