A car driver took a total of 2 hours to make a journey of 75 km. He had a coffee break of half an hour and spent a quarter of an hour stationery in a traffic jam. What was his average speed during the journey ?
The definition of AVERAGE SPEED is:
TOTAL distance traveled divided by the TOTAL time to travel that distance.
The TOTAL distance = 75 km
The TOTAL time = 2 h
therefore by definition the
AVG SPEED = 75/2 = 37.5 km/h
If the driver doesn't move for 1/2 h + 1/4 h = 3/4 h
she must make the TOTAL distance in 2 - 3/4 = 1 1/4 = 1.25 h
to do this, by definition, she must have an
AVG SPEED = 75/1.25 = 60 km/h