A student rides her bicycle home from physics class to get her physics book and then heads back to class. It takes her 21.0 min to make the 12.8 km trip home and 13.0 min to get back to class.

Question

Calculate her average speed for the round-trip. Answer must be converted to km/h

I have no idea how to start this problem. I tried using the v= Delta (X)/ Delta (t) = 12.8/13-21 and I didn't get the right answer.

Answer 1

d = 2 * 12.8 = 25.6 km.

t = (21+13)/60 = 0.567h.

Speed = d/t = 25.6km/0.567h = 45.2 km/h.