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The figure above shows a streetlight that consists of a [#permalink]
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21 Feb 2012, 03:01
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The figure above shows a streetlight that consists of a glass sphere, with center O, placed on top of a vertical pole that is 4 meters high. What is the height QR of the streetlight? (1) The radius of the pole is 6 centimeters. (2) The radius OQ of the sphere is 24 centimeters.
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Re: PT #3 DS 6 [#permalink]
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21 Feb 2012, 03:24
eybrj2 wrote: The figure above shows a streetlight that consists of a glass sphere, with center O, placed on top of a vertical pole that is 4 meters high. What is the height QR of the streetlight?
(1) The radius of the pole is 6 centimeters.
(2) The radius OQ of the sphere is 24 centimeters. There is absolutely no need to actually calculate the height QR. Just notice that the height of a pole (given) and the radius of the pole completely defines (fixes) it. The same way the radius of a sphere completely defines (fixes) it. So, only if we have defined (fixed) pole and defined (fixed) sphere we can be able to say how much below the top of the pole the sphere goes, and we'll be able to calculate QR. Both statements together provide us with the info needed: the radius of the pole and the radius of the sphere. Hence when taken together statements are sufficient. Answer: C. P.S. When dealing with DS problems try to avoid calculations as much as possible. Remember DS problems do not ask you to solve, but rather to determine if you are ABLE to solve and in many cases you can determine that a statement is sufficient without working out all of the math. Hope it's clear.
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Re: PT #3 DS 6 [#permalink]
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21 Feb 2012, 05:12
Bunuel wrote: eybrj2 wrote: The figure above shows a streetlight that consists of a glass sphere, with center O, placed on top of a vertical pole that is 4 meters high. What is the height QR of the streetlight?
(1) The radius of the pole is 6 centimeters.
(2) The radius OQ of the sphere is 24 centimeters. There is absolutely no need to actually calculate the height QR. Just notice that the height of a pole (given) and the radius of the pole completely defines (fixes) it. The same way the radius of a sphere completely defines (fixes) it. So, only if we have defined (fixed) pole and defined (fixed) sphere we can be able to say how much below the top of the pole the sphere goes, and we'll be able to calculate QR. Both statements together provide us with the info needed: the radius of the pole and the radius of the sphere. Hence when taken together statements are sufficient. Answer: C. P.S. When dealing with DS problems try to avoid calculations as much as possible. Remember DS problems do not ask you to solve, but rather to determine if you are ABLE to solve and in many cases you can determine that a statement is sufficient without working out all of the math. Hope it's clear. Hi Bunuel, I'm slightly confused with why do we need the radius of the pole ? If the sphere sits on the pole its one point would touch the pole, hence the height of street lamp would be pole height + sphere diameter Thus B should be sufficient correct? Thanks in advance
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Re: PT #3 DS 6 [#permalink]
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21 Feb 2012, 05:19
boomtangboy wrote: Bunuel wrote: eybrj2 wrote: The figure above shows a streetlight that consists of a glass sphere, with center O, placed on top of a vertical pole that is 4 meters high. What is the height QR of the streetlight?
(1) The radius of the pole is 6 centimeters.
(2) The radius OQ of the sphere is 24 centimeters. There is absolutely no need to actually calculate the height QR. Just notice that the height of a pole (given) and the radius of the pole completely defines (fixes) it. The same way the radius of a sphere completely defines (fixes) it. So, only if we have defined (fixed) pole and defined (fixed) sphere we can be able to say how much below the top of the pole the sphere goes, and we'll be able to calculate QR. Both statements together provide us with the info needed: the radius of the pole and the radius of the sphere. Hence when taken together statements are sufficient. Answer: C. P.S. When dealing with DS problems try to avoid calculations as much as possible. Remember DS problems do not ask you to solve, but rather to determine if you are ABLE to solve and in many cases you can determine that a statement is sufficient without working out all of the math. Hope it's clear. Hi Bunuel, I'm slightly confused with why do we need the radius of the pole ? If the sphere sits on the pole its one point would touch the pole, hence the height of street lamp would be pole height + sphere diameter Thus B should be sufficient correct? Thanks in advance No, it does't "sit" on the pole it's placed IN the circular top of the pole (notice that the sphere is slightly below the top of the pole). Now, consider extreme case when the radius of the pole is more than the radius of the sphere, in that case the sphere will just fall into it. Hope it's clear.
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Collection of Questions: PS: 1. Tough and Tricky questions; 2. Hard questions; 3. Hard questions part 2; 4. Standard deviation; 5. Tough Problem Solving Questions With Solutions; 6. Probability and Combinations Questions With Solutions; 7 Tough and tricky exponents and roots questions; 8 12 Easy Pieces (or not?); 9 Bakers' Dozen; 10 Algebra set. ,11 Mixed Questions, 12 Fresh Meat DS: 1. DS tough questions; 2. DS tough questions part 2; 3. DS tough questions part 3; 4. DS Standard deviation; 5. Inequalities; 6. 700+ GMAT Data Sufficiency Questions With Explanations; 7 Tough and tricky exponents and roots questions; 8 The Discreet Charm of the DS; 9 Devil's Dozen!!!; 10 Number Properties set., 11 New DS set.
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Re: The figure above shows a streetlight that consists of a [#permalink]
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21 Feb 2012, 23:39
Hi Bunuel, Thanks for your reply but I have this question, may be its even silly but in your reply you assumed the pole to be hollow i.e a steel pipe but the question says pole i.e solid pole like a vaulting pole hence the chance of the sphere going into the pole is nil. I dont know how the GMAT defines such terms cause both possibilities exist
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Re: The figure above shows a streetlight that consists of a [#permalink]
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21 Feb 2012, 23:42



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Re: The figure above shows a streetlight that consists of a [#permalink]
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24 Feb 2012, 03:32
I was also confused the part that boomtangboy mentioned above. Bunuel says that the sphere slightly goes into the pole in the picture, but should we solve the problem with the information in the Q, not the picture. The question doesn't say that the sphere slightly goes into the pole. So confusing....



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24 Feb 2012, 03:46



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The figure above shows a streetlight that consists of a [#permalink]
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See that attached picture. We need both radius of the glass sphere and the pole in order to calculate the total height of the combined structure. ANSWER: C eybrj2 wrote: The figure above shows a streetlight that consists of a glass sphere, with center O, placed on top of a vertical pole that is 4 meters high. What is the height QR of the streetlight?
(1) The radius of the pole is 6 centimeters.
(2) The radius OQ of the sphere is 24 centimeters.
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Originally posted by pradeepss on 18 Oct 2014, 13:38.
Last edited by pradeepss on 03 Nov 2014, 21:22, edited 2 times in total.



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Re: The figure above shows a streetlight that consists of a [#permalink]
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27 Oct 2014, 11:51
I am still confused how the information is sufficient.
How do we calculate the c shown above? We only know that a is 6. What is the value of b?



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Re: The figure above shows a streetlight that consists of a [#permalink]
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02 Nov 2014, 17:11
Bunnel, can you help me?



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The figure above shows a streetlight that consists of a [#permalink]
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i updated the picture...please take a look. basically, we know that radius of pole is 6 and radius of the sphere is 24. so we can calculate the partial portion part of the radius of sphere. We can then find the needed information. hope this helps. annie2014 wrote: I am still confused how the information is sufficient.
How do we calculate the c shown above? We only know that a is 6. What is the value of b?
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Re: The figure above shows a streetlight that consists of a [#permalink]
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12 Sep 2017, 00:33
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Ans is C 1) Radius of pole = 6 We dont know the radius of light => unknown for calculating height above pole A,D eliminated 2) Radius of light known but radius of pole unknown => unknown for calculating how much light is inside of pole ie the lower part of sphere B eliminated Combine radius light =24 radius pole = 6 then how much centre of light above pole can be found by pythogoras theorm Ht of centre above pole = √ ( 24^26^2 = h Ht of light RQ = 400+h+24 sufficient C is the Answer
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