Compare the motion of three sailboats. Which sailboat was moving at the lowest speed?

 - a sailboat that moved 135kilometers west in 10hours
 - a sailboat that moved 105kilometers north in 10hours
 - a sailboat that moved 140kilometers south in 10hours
Look at the distance each sailboat moved and the time it took to move that distance. The direction each sailboat moved does not affect its speed.
Notice that each sailboat moved for 10 hours. The sailboat that moved 105 kilometers moved the shortest distance in that time. So, that sailboat must have moved at the lowest speed.