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Theater M has 25 rows with 27 seats in each row. How many of the seats
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20 Jun 2008, 02:27
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Theater M has 25 rows with 27 seats in each row. How many of the seats were occupied during a certain show? (1) During the show, there was an average (arithmetic mean) of 10 unoccupied seats per row for the front 20 rows. (2) During the show, there was an average (arithmetic mean) of 20 unoccupied seats per row for the back 15 rows.
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Re: Theater M has 25 rows with 27 seats in each row. How many of the seats
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20 Jun 2008, 14:02
quantum wrote: Theater M has 25 rows with 27 seats in each row. How many of the seats were occupied during a certain show? (1) During the show, there was an average (arithmetic mean) of 10 unoccupied seats per row for the front 20 rows. (2) During the show, there was an average (arithmetic mean) of 20 unoccupied seats per row for the back 15 rows. Hope you like that one! E
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Re: Theater M has 25 rows with 27 seats in each row. How many of the seats
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20 Jun 2008, 02:38
quantum wrote: Theater M has 25 rows with 27 seats in each row. How many of the seats were occupied during a certain show? (1) During the show, there was an average (arithmetic mean) of 10 unoccupied seats per row for the front 20 rows. (2) During the show, there was an average (arithmetic mean) of 20 unoccupied seats per row for the back 15 rows. Hope you like that one! 1 not suff, because you have info. only about the front 20 rows, the back 5 rows, you dont know whether it is occupied? 2. the same about 10 front rows. I think E
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Re: Theater M has 25 rows with 27 seats in each row. How many of the seats
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20 Jun 2008, 02:49
Yes C cannot be the case  mathematically: Let 010 be o1 and v1 for occupied & Vacant respectively similary for 1020 o2 & v2 and the 2025 as o3 & v3
From Q stem: o1+v1=270, o2+v2=270 & o3+v3=135 Target: To find o1+o2+o3
Now frm st 1: v1+v2=200 insuffi
St2: v2+v3=300 Insuffi
St1+2: We end up with eqs: o1+o2=270 & o2+o3=105  no way can we find the target hence E.



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Re: Theater M has 25 rows with 27 seats in each row. How many of the seats
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20 Jun 2008, 03:03
quantum wrote: But can someone explain in details why C is wrong? Oh, just think that you can figure out! C is combine 1 and 2. You see the intersection between group1(statement1) and group2(statement2) has NOTfixed number of seats unoccupied. You can be sure only that the number of rows in the intersection is 5 rows, but statement1 say average per row is 10 unoccupied and statement2 says everage per row is 20 unoccupied. So the total number of seats unoccupied in 5 rows in the intersection can be 50 or 100 seats. E
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Re: Theater M has 25 rows with 27 seats in each row. How many of the seats
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21 Jun 2008, 02:17
quantum wrote: Theater M has 25 rows with 27 seats in each row. How many of the seats were occupied during a certain show? (1) During the show, there was an average (arithmetic mean) of 10 unoccupied seats per row for the front 20 rows. (2) During the show, there was an average (arithmetic mean) of 20 unoccupied seats per row for the back 15 rows. Hope you like that one! Stem : Total number is seats = 25 * 27 = 675 To find : No of seats occupied 'x'. Option1 ) Avg of 10 unoccupied seats in the front row Number of seats unocupied in the front 20 rows = 200 seats. Total number of occupied seats = 675 200 = 475 . SUFF Option 2 ) Avg of 10 unoccupied seats in the back 15 rows: 20 Total number of seats unoccupied = 20 *15 = 300 Total number of occupied seats = 675 300 = 375 . SUFF IMO = D



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Re: Theater M has 25 rows with 27 seats in each row. How many of the seats
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10 Jan 2010, 10:09
we know that there were 17*20 people in the first 20 rows
and
7*15 people in the last 15 rows
however there is an overlap of 10 rows between the first 20 and the last 15 rows.
to know how many people occupied those 10 rows, additional information is needed.
hence answer is E
a venn diagram will help in this question



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Re: Theater M has 25 rows with 27 seats in each row. How many of the seats
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26 Apr 2013, 22:53
Theater M has 25 rows with 27 seats in each row. How many of the seats were occupied during a certain show?(1) During the show, there was an average (arithmetic mean) of 10 unoccupied seats per row for the front 20 rows.Clearly not sufficient, no info about other rows (2) During the show, there was an average (arithmetic mean) of 20 unoccupied seats per row for the back 15 rows.Clearly not sufficient, no info about other rows 1+2)With 1 we know that there are 200 unoccupied in the first 20 rows, with 2 we know that there are 300 unoccupied in the last 15 rows. Because we don't know how many seats there are in the common part (rows 1020) both statements are still not sufficient. EHope it's clear, let me know
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Re: Theater M has 25 rows with 27 seats in each row. How many of the seats
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11 Oct 2013, 06:32
sagarsabnis wrote: Theater M has 25 rows with 27 seats in each row. How many of the seats were occupied during a certain show? (1) During the show, there was an average (arithmetic mean) of 10 unoccupied seats per row for the front 20 rows. (2) During the show, there was an average (arithmetic mean) of 20 unoccupied seats per row for the back 15 rows. Let me try to explain this one. So we are asked how many seats occupied. Statement 1  Clearly insfficient, we only have information about 20 rows Statement 2 Same here, we are missing information on other rows Now both (1) and (2) together  So we have from the 1st statement that the total number of seats for the first 20 rows that were unnocupied totaled 200. And also the unnocpied for the back 15 rows were 300. But we have an overlap here between rows. If we don't have more information it will be impossible to know. Imagine a venn diagram and visualize the intersection between both. As long as you don't have the exact value for the intersection it will be impossible to know the total number of unnocupied seats and hence know what the occupied seats are. I think this will do for now. Hope it helps



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Re: Theater M has 25 rows with 27 seats in each row. How many of the seats
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17 Jan 2015, 13:09
E
Try seeing extremes.... statements didnt concretize the seating pattern so
divide rows into 3 parts first 10 + 10 + 5 rows
extreme 1: Middle set takes average of say 30 (higher side)
first 10 has average of <10 unoccupied (say 5..u can calculate actual possibility) + next 10 say abt 30 + last 5 has average of <20 unoccupied => would have a overall count on lower side
extreme 2: Middle set takes average of say 5
first 10 has average of >10 unoccupied (say 20..u can calculate actual possibility) + next 10 say abt 5 + last 5 has average of >20 unoccupied => would have a overall count on higher side
The logic is the middle set can act as cushion so we have a range of possibilities
Had their been no overlap....then we can find the total
Hope it helps..!



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Re: Theater M has 25 rows with 27 seats in each row. How many of the seats
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17 Jan 2015, 13:09
E
Try seeing extremes.... statements didnt concretize the seating pattern so
divide rows into 3 parts first 10 + 10 + 5 rows
extreme 1: Middle set takes average of say 30 (higher side)
first 10 has average of <10 unoccupied (say 5..u can calculate actual possibility) + next 10 say abt 30 + last 5 has average of <20 unoccupied => would have a overall count on lower side
extreme 2: Middle set takes average of say 5
first 10 has average of >10 unoccupied (say 20..u can calculate actual possibility) + next 10 say abt 5 + last 5 has average of >20 unoccupied => would have a overall count on higher side
The logic is the middle set can act as cushion so we have a range of possibilities
Had their been no overlap....then we can find the total
Hope it helps..!



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Re: Theater M has 25 rows with 27 seats in each row. How many of the seats
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10 Mar 2015, 04:58
Bunuel ..Karishma and other experts !
Is there a faster and a more logical way to solve this problem (or similar type of problems)?
Regards, SR



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Re: Theater M has 25 rows with 27 seats in each row. How many of the seats
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10 Mar 2015, 21:30
Hi solitaryreaper, The type of situation that this DS question is based on is relatively rare, but the most efficient way to deal with it is to think about the "extreme" possibilities in the numbers. I assume that you recognized that each Fact was insufficient on its own (since neither Fact gives you enough information about ALL 25 rows. When combining Facts, you have to recognize that there's an "overlap"  the "front 20 rows" mentioned in Fact 1 and the "back 15 rows" mentioned in Fact 2 include a series of 10 rows that are a part of BOTH calculations (remember that there are only 25 rows in TOTAL). It's in those 10 overlapping rows that you can greatly impact the calculations. What if ALL of those seats were full? What if ALL of those seats were empty? In those two examples, you will find 2 different answers to the question. If you've comfortable drawing pictures and 'visualizing' the calculations, you can actually avoid most of the 'math' altogether. GMAT assassins aren't born, they're made, Rich
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Re: Theater M has 25 rows with 27 seats in each row. How many of the seats
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17 Mar 2015, 00:38
EMPOWERgmatRichC wrote: Hi solitaryreaper,
The type of situation that this DS question is based on is relatively rare, but the most efficient way to deal with it is to think about the "extreme" possibilities in the numbers.
I assume that you recognized that each Fact was insufficient on its own (since neither Fact gives you enough information about ALL 25 rows. When combining Facts, you have to recognize that there's an "overlap"  the "front 20 rows" mentioned in Fact 1 and the "back 15 rows" mentioned in Fact 2 include a series of 10 rows that are a part of BOTH calculations (remember that there are only 25 rows in TOTAL).
It's in those 10 overlapping rows that you can greatly impact the calculations. What if ALL of those seats were full? What if ALL of those seats were empty? In those two examples, you will find 2 different answers to the question. If you've comfortable drawing pictures and 'visualizing' the calculations, you can actually avoid most of the 'math' altogether.
GMAT assassins aren't born, they're made, Rich Thanks Rich, that helps! I was looking for a logical approach to tackle such problems under 2 minutes. I think it's not always fruitful to approach such problems in pure mathematical way(because one might end up loosing precious time and energy) . That's where GMAT surprise you by throwing such problems that demand for a more logical approach. IMO such problems and methodologies should be discussed in a greater number ! Regards, Arun



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Re: Theater M has 25 rows with 27 seats in each row. How many of the seats
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18 Mar 2015, 11:40
Hi Arun, You've hit on an important point  knowing MORE than one way to approach questions can be quite helpful on Test Day. For most of your life, you were taught just 1 way to approach a question. When you took a test in school, you were supposed to use that 1 way and so you studied just that 1 way. On the GMAT though, many questions are designed to 'reward' a Test Taker for being is a critical thinker or patternmatcher more than for being a mathematician. During your studies, it's important to practice more than one approach so that you have the flexibility on Test Day to decide which method is easiest/fastest. Another thing worth noting is that you should NOT be trying to answer every Quant question within 2 minutes. The AVERAGE amount of time that you'll spend per question over the course of the entire Quant section is about 2 minutes, but your GOAL is actually to work in an efficient fashion. A question might require 1 minute or 3 minutes  and that's fine as long as you're not wasting time. If this question takes you 2.5 minutes, then that's not a problem. GMAT assassins aren't born, they're made, Rich
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