I am 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!