I have already done this problem enough times forwards and backwards to get the answer, so this is more of a theory question rather than help with homework. The equation for Vavg.=displacement/time or deltaX/deltaT. This equate to V=(X2-X1)/(T2-T1), correct? In working through a problem, the correct version of this equation ended up being: V=(X1-X2)/(T1+T2). Here's the question: In reaching her destination, a backpacker walks with an average velocity of 1.34m/s, due west. This average velocity results because she hikes for 6.44km with an average velocity of 2.68m/s, due west, turns around, and hikes with an average velocity of 0.447m/s, due east. How far east did she walk? In fact, here's a link to the solution to the problem that I found: http://www.cramster.com/physics-answers-5-315022-cpi0.aspx My question is this: How was that form of the equation derived? I solved this many times using the standard equation and was doing the entire procedure correctly...but was getting the wrong answer as I was using my initial equation rather than the version I have mentioned here. Can someone explain to me what the reasoning is behind this?