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The first flight out of Phoenix airport had a late departure
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12 Jan 2012, 07:51
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62% (01:25) correct 38% (01:31) wrong based on 66 sessions
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The first flight out of Phoenix airport had a late departure. If the next three flights departed ontime, minimum how many subsequent flights need to depart from Phoenix ontime, for the airport's ontime departure rate to be higher than 90%? A. 6 B. 7 C. 9 D. 10 E. 11 I will see what is the quickest way to solve it then I will provide the explanation
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Re: The first flight out of Phoenix airport had a late departure
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13 Jan 2012, 04:28
1/(3+x) <= 0.1 => x => 7 Therefore (B)
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Re: The first flight out of Phoenix airport had a late departure
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Updated on: 07 Mar 2012, 06:38
My approach:
If the first (one) flight had a late departure, then 1 flight out of 1 flight had a late departure (100% of the flights so far). Then, the stem says that the next 3 flights departed ontime, meaning that 1 out of 4 flights had a late departure (25% of the flights so far). Therefore, following this logic, if we add another 6 ontime planes, we will know that 1 out of 10 flights had a late departure (thus 10% was late and 90% was ontime).
The question asks how many subsequent flights need to depart from Phoenix ontime, for the airport's ontime departure rate to be HIGHER than 90%. As we have seen so far, if 6 subsequent planes were ontime, we would have a rate of EXACTLY 90% of late departure. Therefore, for the airport's ontime departure rate to be HIGHER than 90%, we need 7 subsequent planes to be ontime (1 out of 11 had a late departure or aprox. 9% of the flights  the remaining 91% is the rate of ontime flights).
Ans: B
Originally posted by pedroca on 06 Mar 2012, 22:25.
Last edited by pedroca on 07 Mar 2012, 06:38, edited 1 time in total.



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Re: The first flight out of Phoenix airport had a late departure
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06 Mar 2012, 22:55
manalq8 wrote: The first flight out of Phoenix airport had a late departure. If the next three flights departed ontime, how many subsequent flights need to depart from Phoenix ontime, for the airport's ontime departure rate to be higher than 90%?
A. 6 B. 7 C. 9 D. 10 E. 11
I will see what is the quickest way to solve it then I will provide the explanation The following approach might be the easiest one and less error prone. We need ontime departure rate to be higher than 9/10, so it should be at least 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 103=7 subsequent flights need to depart ontime. Answer: B.
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Re: The first flight out of Phoenix airport had a late departure
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11 Feb 2013, 10:18
Bunuel wrote: manalq8 wrote: The first flight out of Phoenix airport had a late departure. If the next three flights departed ontime, how many subsequent flights need to depart from Phoenix ontime, for the airport's ontime departure rate to be higher than 90%?
A. 6 B. 7 C. 9 D. 10 E. 11
I will see what is the quickest way to solve it then I will provide the explanation The following approach might be the easiest one and less error prone. We need ontime departure rate to be higher than 9/10, so it should be at least 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 103=7 subsequent flights need to depart ontime. Answer: B. one flight was already late & 3 flight were on time departure so now to have a ontime departure rate to be higher than 9/10, 3 on time + 6 yet to be on time = 9 on time. total of 10, 9 on time but it not higher than 9/10 so so we went for 7 by considering 10/11?



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Re: The first flight out of Phoenix airport had a late departure
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11 Feb 2013, 10:31
FTG wrote: Bunuel wrote: manalq8 wrote: The first flight out of Phoenix airport had a late departure. If the next three flights departed ontime, how many subsequent flights need to depart from Phoenix ontime, for the airport's ontime departure rate to be higher than 90%?
A. 6 B. 7 C. 9 D. 10 E. 11
I will see what is the quickest way to solve it then I will provide the explanation The following approach might be the easiest one and less error prone. We need ontime departure rate to be higher than 9/10, so it should be at least 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 103=7 subsequent flights need to depart ontime. Answer: B. one flight was already late & 3 flight were on time departure so now to have a ontime departure rate to be higher than 9/10, 3 on time + 6 yet to be on time = 9 on time. total of 10, 9 on time but it not higher than 9/10 so so we went for 7 by considering 10/11? Yes, you can say so.
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Re: The first flight out of Phoenix airport had a late departure
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19 Sep 2013, 10:25
how did you calculate 10/11?



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Re: The first flight out of Phoenix airport had a late departure
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26 Dec 2013, 10:46
manalq8 wrote: The first flight out of Phoenix airport had a late departure. If the next three flights departed ontime, how many subsequent flights need to depart from Phoenix ontime, for the airport's ontime departure rate to be higher than 90%?
A. 6 B. 7 C. 9 D. 10 E. 11
I will see what is the quickest way to solve it then I will provide the explanation 3+x/4+x >9/10 x>6 Hence B is our best choice Cheers! J



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Re: The first flight out of Phoenix airport had a late departure
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26 Dec 2013, 11:21
theGame001 wrote: how did you calculate 10/11? here is my approach to this question. Let the total number of flights be 'x'. On time departure rate should be more than 90%. it is said that 1 flight is late.... so out of x flights is 1 flight is late remaining (x1) flights will be ontime... so \(\frac{(x1)}{x}*100=90\) solving for x we get 10...... but remember we want ontime departure rate to be more than 90%, not exactly 90%..... so minimum number of flights to take off is 11..... since first one is late and remaining 3 left so the next 7 flights should also be ontime..... So answer is 7...



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Re: The first flight out of Phoenix airport had a late departure
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17 Mar 2018, 16:56
I agree with the shortcut proposed by bb. However, the method requires the sensibility in math, and I do not like it. The other easy way is to test each answer, and start with A, then B,... I think the question asks about the minimum subsequent flights; otherwise, answer can be infinite.




Re: The first flight out of Phoenix airport had a late departure
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17 Mar 2018, 16:56






