• anonymous
A bus covered 400km distance between points A and B at a certain speed. On the return trip, the biker traveled at the same speed for 2 hours and then increased the speed by 10km an hour until it reached A, this spending 20 fewer minutes on the return treip. How long did the return trip take?
  • Stacey Warren - Expert
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  • jamiebookeater
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  • IrishBoy123
you need to start building your own equations describing what is happening. just distance = speed * time stuff, but building in the subtleties of this situation. for example you might start by letting v = the speed on the outward leg. therefore you already have the equation 400 = v * T1 where T1 is the duration of the outward leg. If the total duration of the return leg is T2, you also have T2 = T1 - 1/3 (the 1/3 being the third of an hour you saved by going faster. You also know that if the final part at the higher speed is called t, then 400 = 2 * v + t *( v + 10). that's 2 hours at speed v, then travelling at 10 + v for the last period of time t. this is all you need to solve this - plus of course cranking through the equations and solving. there may be other ways of building the basic equations. just give it a go, either the way i suggest or using your own formula. just be sure to keep the units consistent. my formula work in kilometres, hours and km/hr.

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