The number of flights leaving a certain airport doubles during every one-hour period between its 9 am 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 am and 10 am, how many flights left airport between 2 pm and 4 pm?
Solution
Correct Answer: Option D
Doubles every hour between 9 and 12, doubles every 2 hours after 12
9-10 : 4 flights : given
10-11: 8 flights : double the number between 9-10
11-12: 16 flights : double the number between 10 : 11
12-2 : 32 flights : etc.
2-4 : 64 flights
64 flights left the airport in the period from 2pm to 4pm.
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