How do you find the average acceleration in a velocity-time graph?

The acceleration in a velocity time graph is given by its' gradient.

Assuming this is a straight line graph, you can find the gradients using the formula:

x1 - x2

y1-y2

where (x1,y1) and (x2, y2) are two points on the straight line.

If the graph has several sections, simply use the above method to find the acceleration for each part, then find the average using the usual method of adding the set of values together and dividing by the number of values.

Acceleration is equal to the gradient. To find the average acceleration draw a line from the beginning to the end and then find the gradient of that line. Typically you would do this by forming a triangle and working out the change in the y direction (height of triangle) and the change in the x direction (base of the triangle) then divide the change in y by the change in x.