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Difficulty:
15%
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Question Stats:
79% (01:31) correct
21%
(02:10)
wrong
based on 103
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The number of flights leaving a certain airport doubles during every one-hour period between its 9 A.M. opening and noon; after noon, the number of flights leaving from the airport doubles during every two-hour period. If 4 flights left from the airport between 9 and 10 a.m., how many flights left the airport between 2 and 4 P.M.?
(A) 32
(B) 48
(C) 64
(D) 128
(E) 256
(A) 32
(B) 48
(C) 64
(D) 128
(E) 256
SajjadAhmad
Hi,
9 to 10 = X
10 to 11 = 2X
11 to Noon = 4X
Noon to 2 P.M. = 8X
2 P.M. to 4 P.M. = 16X
and X = 4 so 16X = 64
Ans. C
It's interesting to note that the right answer can't be A or B, since it needs to be a power of 2. (If you double 4 repeatedly, you'll only ever end up with powers of 2). This could be a good basis for a fast guess.
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Chemerical71
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[quote="SajjadAhmad"]The number of flights leaving a certain airport doubles during every one-hour period between its 9 A.M. opening and noon; after noon, the number of flights leaving from the airport doubles during every two-hour period. If 4 flights left from the airport between 9 and 10 a.m., how many flights left the airport between 2 and 4 P.M.?
(A) 32
(B) 48
(C) 64
(D) 128
(E) 256[/quote
let from 9 am to 10 am =X
given that for every hour it doubles from 9 to 12 am, after that for every two hours f. leaving doubles thus X+2x+4x+8x+16x
thus, from 2pm to 4 pm = 16x
given that From 9am to 10 am = 4.
therefor, 16*4= 64( C)
Could you please tell the source of the question.
(A) 32
(B) 48
(C) 64
(D) 128
(E) 256[/quote
let from 9 am to 10 am =X
given that for every hour it doubles from 9 to 12 am, after that for every two hours f. leaving doubles thus X+2x+4x+8x+16x
thus, from 2pm to 4 pm = 16x
given that From 9am to 10 am = 4.
therefor, 16*4= 64( C)
Could you please tell the source of the question.
ScottTargetTestPrep
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Target Test Prep Representative
Joined: 14 Oct 2015
Last visit: 11 Sep 2026
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Expert reply
Posts: 22,738
SajjadAhmad
Solution:
We can tabulate the number of planes every hour before noon and every two hours after noon:
Between 9 am and 10 am: 4
Between 10 am and 11 am: 8
Between 11 am and noon: 16
Between noon and 2 pm: 32
Between 2 pm and 4 pm: 64
Answer: C
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