Question 214838
Car A is traveling at 20 miles per hour. Car B is one mile behind, following at 30 miles per hour. A fly can move 40 miles per hour. The fly begins on the front bumper of car B and flys back and forth between the two cars. How many miles will the fly travel before it is crushed in the collision? 
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Car B is gaining on car A at 10 mph (30 - 20).  To overtake car A 1 mile ahead at 10 mph will take 1/10 hours.
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The fly will go back and forth at 40 mph for 1/10 of an hour.
40*(1/10) = 4 miles.