A cheetah can run at a top speed of 60 mph.  The gazelle can run for speeds of up to 40 miles per hour.  If one mile per hour is about 1.5 feet per second, then how many seconds would it take for a cheetah traveling at top speed to catch up to a fleeing gazelle also running at top speed if the two animals were initially 210 feet apart and they both traveled in the same direction?
60 mph is 60*1.5=<<60*1.5=90>>90 feet per second.
40 mph is 40*1.5=<<40*1.5=60>>60 feet per second.
Thus, for every second, the cheetah advances on the gazelle by 90-60=<<90-60=30>>30 feet per second.
To close on a distance of 200 feet, it would take the cheetah 210/30=7 seconds to catch the gazelle.
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