The Super-fly
A train leaves São Paulo destined to Rio de Janeiro with speed of 60 Km/h. At the same time, leaves Rio de Janeiro destined to São Paulo, a second train with speed of 40 Km/h. In front of this train and at the same time, a super-fly goes with speed of 70 Km/h. It goes to meet of the train who comes from São Paulo and, after meeting, come back destined to Rio de Janeiro untill meet the second train, and so on untill when the both trains clash. Admitting the distance São Paulo - Rio de Janeiro be equal to 500 Km, what the total distance traveled, in Kilometers, by the Super-fly in this zig-zag untill be died smashed?
The answer is 350.
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1 solution
The relative speed of the train coming at each other is ( 60+40) km/h. The time it takes before they collide= total distance between them/ relative speed= 500km/100km/h= 5 hours.
In 5 hours, the fly would have travelled ( 5 hr x 70km/h)= 350 km.