1. The problem statement, all variables and given/known data A locomotive travels on a straight track at a constant speed of 40 mi/h, then reverses direction and returns to its starting point, traveling at a constant speed of 60 mi/h. What is the average speed for the round-trip? 2. Relevant equations avgS = distance/time t = d/40 3. The attempt at a solution avgS = 2d/(t+40/60(t)) = 2d/(t+(2/3)t) = 2(t/40)/(t+(2/3)t) = (t/20)/(t+(2/3)t) I don't really know what to do after this point. The solution manual has the steps for the solution as: avgS = 2d/(t+(2/3)t) = 80t/(t+(2/3)t) = 48 mi/h I have no idea how they got to the last step. Any help is greatly appreciated.