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M06#3

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Senior Manager
Status: Do and Die!!
Joined: 15 Sep 2010
Posts: 326
Followers: 1

Kudos [?]: 506 [0], given: 193

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23 Jan 2011, 20:22
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

official Explanation :

[Reveal] Spoiler:
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 don't understand how many total flights we have ?
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I'm the Dumbest of All !!

Kaplan GMAT Instructor
Joined: 21 Jun 2010
Posts: 148
Location: Toronto
Followers: 45

Kudos [?]: 197 [1] , given: 0

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23 Jan 2011, 21:04
1
KUDOS
shrive555 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

I don't understand how many total flights we have ?

Hi,

we're being asked about a percent, so let's jot down the percent formula:

% = (part/whole) * 100%

In this question, the whole is the total number of flights and the part is the number that depart on time.

Of the first 4 flights, we know 1 is late and 3 are on time. So, the % on time out of the first 4 is 3/4 = 75%.

To satisfy the question's criterion, we need that on time rate to be greater than 90%. In other words:

(# on time)/(total # of flights) > 9/10

Since we only have 1 flight that's late, the quickest way to get more than 9/10 on time is to have every flight on time from here on out. Since 9/10 is too small, we need 10/11 to get greater than a 90% rate. We've had 4 flight so far, so we need 7 more flight to get to 10/11 - choose (B).
Senior Manager
Status: Do and Die!!
Joined: 15 Sep 2010
Posts: 326
Followers: 1

Kudos [?]: 506 [0], given: 193

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25 Jan 2011, 09:57
THanks a lot stuart
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Re: M06#3   [#permalink] 25 Jan 2011, 09:57
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M06#3

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