Iam having major trouble calculating the average speed for things. an example of a question would be, rachel travelled 240 km in 4 hours by train and then travelled 120 km in 3 hours by car and 3 km in 1/2 hour by cycle. what is the average speed during the whole journey? i have a test over this tomorrow and my teachers doesn't explain anything very well.

The average speed is      (distance covered) / (time to cover the distance) .

For example:

The average speed for the 'car' part of her trip is

                  (distance covered in the car) / (time in the car) =

                                             (120 km) / (3 hours) = 40 km per hr.

Answering the question:

Average speed for the whole journey is

  (distance covered on the journey) / (time spent on the whole journey) =

                      (240 + 120 + 3) km /  (4 + 3 + 1/2) hours  = 

                                      363 km  /  7.5 hours  =  48.4 km per hour

Good luck on the test !

Work is reduced while time is decreased