If you have a velocity -time graph the area under it is the distance traveled between t1 and t2
The average velocity is
[tex]{\rm{average velocity = }}\frac{{{\rm{total distance}}}}{{{\rm{total time}}}}{\rm{ = }}\frac{{{\rm{Area under graph between }}{{\rm{t}}_{\rm{1}}}{\rm{and }}{{\rm{t}}_{\rm{2}}}}}{{{{\rm{t}}_{\rm{2}}}{\rm{ - }}{{\rm{t}}_{\rm{1}}}}}[/tex]