Compare the motion of two fish. Which fish was moving at a lower speed?

 - a fish that moved 10miles in 10hours
 - a fish that moved 30miles in 10hours
Look at the distance each fish moved and the time it took to move that distance.
One fish moved 10 miles in 10 hours.
The other fish moved 30 miles in 10 hours.
Notice that each fish spent the same amount of time moving. The fish that moved 10 miles moved a shorter distance in that time. So, that fish must have moved at a lower speed.