Compare the motion of three speedboats. Which speedboat was moving at the lowest speed?

 - a speedboat that moved 290kilometers west in 5hours
 - a speedboat that moved 510kilometers east in 5hours
 - a speedboat that moved 215kilometers east in 5hours
Look at the distance each speedboat moved and the time it took to move that distance. The direction each speedboat moved does not affect its speed.
Notice that each speedboat moved for 5 hours. The speedboat that moved 215 kilometers moved the shortest distance in that time. So, that speedboat must have moved at the lowest speed.