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M06 P.S problem

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Manager
Joined: 02 Oct 2008
Posts: 57

Kudos [?]: 75 [0], given: 0

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12 Dec 2009, 11:33
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%?

6
7
9
10
11
In order to reach an above 90% on-time departure rate, the airport will need to have 10 out of 11 flights depart on time, so 7 more is the answer. If only 6 more depart on-time, it will be 90% exactly, and that's not enough.

I am not sure why number 11 was chosen to solve the problem ? why other random numbers were no considered solve the above one? Please explain

Kudos [?]: 75 [0], given: 0

VP
Joined: 05 Mar 2008
Posts: 1467

Kudos [?]: 307 [0], given: 31

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12 Dec 2009, 11:54
tania 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%?

6
7
9
10
11
In order to reach an above 90% on-time departure rate, the airport will need to have 10 out of 11 flights depart on time, so 7 more is the answer. If only 6 more depart on-time, it will be 90% exactly, and that's not enough.

I am not sure why number 11 was chosen to solve the problem ? why other random numbers were no considered solve the above one? Please explain

9/10 = 90%
but we want over 90%
10/11 > 90%

Kudos [?]: 307 [0], given: 31

Re: M06 P.S problem   [#permalink] 12 Dec 2009, 11:54
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M06 P.S problem

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