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M06-03

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Math Expert
Joined: 02 Sep 2009
Posts: 50007

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16 Sep 2014, 00:26
00:00

Difficulty:

45% (medium)

Question Stats:

58% (01:06) correct 42% (01:03) wrong based on 183 sessions

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The first flight out of Phoenix airport had a late departure. If the next three flights departed on-time, how many subsequent flights need to depart from Phoenix on-time, for the airport's on-time departure rate to be higher than 90%?

A. 6
B. 7
C. 9
D. 10
E. 11

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Math Expert
Joined: 02 Sep 2009
Posts: 50007

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16 Sep 2014, 00:26
Official Solution:

The first flight out of Phoenix airport had a late departure. If the next three flights departed on-time, how many subsequent flights need to depart from Phoenix on-time, for the airport's on-time departure rate to be higher than 90%?

A. 6
B. 7
C. 9
D. 10
E. 11

We need on-time departure rate to be higher than $$\frac{9}{10}$$, so it should be at least $$\frac{10}{11}$$, which means that 10 out of 11 flights must depart on time. Since for now 3 out of 4 flights departed on time then $$10-3=7$$ subsequent flights need to depart on-time.

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Joined: 27 Aug 2014
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11 Feb 2015, 14:36
I think this question is poor and not helpful.
it is not clear "subsequent" to which number: the 1 flight late, or the 3 flight on time.
can be formulated "how many more subsequent flights..."
Intern
Joined: 09 Feb 2015
Posts: 20

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02 May 2015, 07:34
1
Let x be subsequent flights need to depart from Phoenix on-time.
To the airport's on-time departure rate to be higher than 90%: 3+x/4+x >0.9 => 0.1x>0.6 => x>6, x=7.
Is it right.
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Joined: 17 Mar 2014
Posts: 5

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16 Sep 2015, 03:18
I think this is a poor-quality question and I don't agree with the explanation.
Math Expert
Joined: 02 Sep 2009
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16 Sep 2015, 03:42
prodigypringle wrote:
I think this is a poor-quality question and I don't agree with the explanation.

Please elaborate WHY do you think that the question is of poor-quality. Thank you.
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15 Oct 2015, 11:24
This is a very straightforward question. For the % to be > 90, we need atleast 10 flights on time (as 1 was delayed). 3 of those 10 were on-time, hence 7 more are required.
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Joined: 14 Jun 2014
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04 Apr 2016, 06:06
I think this is a poor-quality question and I agree with explanation. somehow agree . I think "minimum" should be added be fore on-time because otherwise 9,10,11 subsequent flights also make a on-time departure rate higher then 90%
Math Expert
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04 Apr 2016, 06:19
deospaima wrote:
I think this is a poor-quality question and I agree with explanation. somehow agree . I think "minimum" should be added be fore on-time because otherwise 9,10,11 subsequent flights also make a on-time departure rate higher then 90%

Hi,
1) firstly I really don't understand why it is a Poor Q. It is a very normal Q.
2) Yes, minimum would have made things more clearer. BUT when we sayhow many subsequent flights need to depart from Phoenix on-time, for the airport's on-time departure rate to be higher than 90%?, I think it conveys the same meaning..
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Intern
Joined: 14 Jun 2014
Posts: 7

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04 Apr 2016, 09:32
when you send feedback from CATs in Gmat Club if you tick "poor questions" it automatically ads this to the thread..so actually I don't find it a poor questions , I just think it should be more clear. honestly I don't agree with this :

BUT when we sayhow many subsequent flights need to depart from Phoenix on-time, for the airport's on-time departure rate to be higher than 90%?, I think it conveys the same meaning..

in GMAT questions I think you shouldn't have 2 answers that verify the conditions..and here we have multiple ones..just my opinion
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Joined: 23 Apr 2016
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10 Jun 2016, 09:53
Bunuel wrote:
prodigypringle wrote:
I think this is a poor-quality question and I don't agree with the explanation.

Please elaborate WHY do you think that the question is of poor-quality. Thank you.

Bunuel, I believe this is a good question however it seems to me that "subsequent" is used in a vague manner. Subsequent from the first flight (10-4=6 additional on-time flights needed to bring % to 90) or subsequent from the FIRST on-time flight (10-3=7 additional flights needed to bring percentage to 90)?

I chose 6 as my answer because I was counting all subsequent flights from the first late departure.

Aside from this I do think it is a good question
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Joined: 04 Jan 2015
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25 Aug 2016, 14:10
I think this question tests your verbal skills also , and i got it wrong too .

But for those who believe that the language is inappropriate , its not.

If the next three flights departed on-time, how many subsequent flights need to depart from Phoenix on-time, for the airport's on-time departure rate to be higher than 90%?
The underlined portion is clearly making a play on the "next three flights" , and the significance of the word "need" is to mean that we "need" to find the minimum number of more subsequent flights.
I hope everyone got my point.
Intern
Joined: 26 May 2016
Posts: 20
GMAT 1: 640 Q49 V30

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02 May 2017, 03:13
2
Bunuel wrote:
The first flight out of Phoenix airport had a late departure. If the next three flights departed on-time, how many subsequent flights need to depart from Phoenix on-time, for the airport's on-time departure rate to be higher than 90%?

A. 6
B. 7
C. 9
D. 10
E. 11

Here's my take on this:

Current stat:
1 on time
3 late

current % of on time departure: 3/4 = 75%

We need >90%, hence let's keep adding more flights that departed on time.

(3+1)/(4+1) = 4/5 = 80% not over to 90%
(3+2)/(4+2) = 5/6 not over to 90%
(3+3)/(4+3) = 6/7 not over to 90%
(3+4)/(4+4) = 7/8 not over to 90%
(3+5)/(4+5) = 8/9 not over to 90%
(3+6)/(4+6) = 9/10 = 90% not over to 90%
(3+7)/(4+7) = 10/11 just over to 90%

Director
Joined: 02 Sep 2016
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06 Sep 2017, 02:24
Bunuel and abhimahna

What I understood from this question was:
Total= 4 flights (till now)
On time= 3

Therefore 3/4*100= 75% on time

For this percentage to be >90%:

If 6 more flights take off on time, then there will be total 6+3 flights that took off on time.

Total= 6+3+1= 10
On time= 9
Percentage= 9/10*100 = 90%

What did I miss? Is it the "subsequent" information that I misinterpreted?
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Director
Joined: 02 Sep 2016
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06 Sep 2017, 02:26
I think I somewhat get it:

We need more than 90% and option A gives exactly 90%.
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Senior Manager
Joined: 17 Mar 2014
Posts: 383

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02 Jan 2018, 22:17
Bunuel wrote:
Official Solution:

The first flight out of Phoenix airport had a late departure. If the next three flights departed on-time, how many subsequent flights need to depart from Phoenix on-time, for the airport's on-time departure rate to be higher than 90%?

A. 6
B. 7
C. 9
D. 10
E. 11

We need on-time departure rate to be higher than $$\frac{9}{10}$$, so it should be at least $$\frac{10}{11}$$, which means that 10 out of 11 flights must depart on time. Since for now 3 out of 4 flights departed on time then $$10-3=7$$ subsequent flights need to depart on-time.

Bunuel, could you explain how did you come to 10/11. I am not able to get above highlighted red part.
Math Expert
Joined: 02 Sep 2009
Posts: 50007

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02 Jan 2018, 23:27
ammuseeru wrote:
Bunuel wrote:
Official Solution:

The first flight out of Phoenix airport had a late departure. If the next three flights departed on-time, how many subsequent flights need to depart from Phoenix on-time, for the airport's on-time departure rate to be higher than 90%?

A. 6
B. 7
C. 9
D. 10
E. 11

We need on-time departure rate to be higher than $$\frac{9}{10}$$, so it should be at least $$\frac{10}{11}$$, which means that 10 out of 11 flights must depart on time. Since for now 3 out of 4 flights departed on time then $$10-3=7$$ subsequent flights need to depart on-time.

Bunuel, could you explain how did you come to 10/11. I am not able to get above highlighted red part.

We need (on-time departures)/(total departures) to be greater than 9/10. Next, fraction, which is greater than 9/10 (having both numerator and denominator integers) is 10/11:

9/10 < 10/11 < 11/12 < ...
9/10 < 10/11 < 91/100 < ...
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