Keenan needs to write an essay that is 1200 words. Her essay is due at midnight. She writes 400 words per hour for the first two hours. After that, she writes 200 words per hour. How many hours before the deadline does she need to start to finish on time?
In the first two hours, Keenan writes 800 words because 400*2=<<400*2=800>>800.
After that, she still needs to write 400 words because 1200-800=<<1200-800=400>>400.
Since she writes 200 words per hour, she will take 2 hours to write the last 400 words because 400/200=<<400/200=2>>2.
Thus, she needs to start 4 hours before the deadline because 2+2=<<4=4>>4.
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