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 Homework Statement:

A ball moves in a straight line ( the xaxis). The graph shows this ball's velocity as a function of time.
a) What are the ball's average speed and average velocity during the first 3.0 s?
b) Suppose that the ball moved in such a way that the graph segment after 2.0 s was 3.0 m/s instead of +3.0 m/s. Find the ball's average speed and average velocity in this case.
 Relevant Equations:
 ##v_{avx}=\frac{v_3+v_0}{2}##
So thing that confusses me, is what is the difference regarding the calculation of speed and velocity? In think I should use the formula I wrote above to find the average velocity, but I don't understand what the formula for average speed will be then. By the way, when using the formula above, should I use the values instead of two?
##\frac{v_3+v_2+v_1}{3}=\frac{2+2+3}{3}=2.33 m/s ##
I really appreciate some help! :)