A motorist drives north at 28m/s for 5 minutes, turns around and then drives 25m/s in the opposite direction for 3 minutes calculate the average speed and the average velocity for the whole journey

Answer 1

avg speed = distance/time = (28*5 + 25*3)/(5 + 3) = 26.875 m/s
avg velocity = (28*5 - 25*3)/(5+3) = 8.125 m/s
where the + value indicates a net north velocity

Yes, I know that 5 minutes is 5*60=200 seconds, but since the factor of 60 occurs both in the top and bottom, it cancels out. As written, the units are (m/s*min)/(min), which equates to m/s.