What rocks but does not roll?

Walking home one day, you take a short cut along the train tracks. The tracks cross a narrow bridge over a deep gorge. At the point you are 3/8 of the way across the bridge, you hear the train whistle somewhere behind you. You charge across the bridge, and jump off the track as the train is about to run you down. As it happens, if you had gone the other way, you would have reached safety just before being run over as well. If you can run ten miles per hour, how fast is the train moving?

Find the four digit number in which the first digit is one fourth of the last digit, the second digit is 6 times the first digit, and the third digit is the second digit plus 3. What is it?

A man buys a rope from a woman for $3.00 and hands the woman a $10 bill. The woman goes into the grocery store next door to get change. She returns and gives the man $7.00. After the man leaves, the clerk from the store comes and says, "Hey, that was a counterfeit bill you gave me." The woman gives the clerk a good bill.

How much has the woman lost?

Round as a button, Deep as a well. If you want me to talk, You must first pull my tail.

What am I?

The head of a whale is six feet long; his tail is as long as his head and half his body, and his body is half of his whole length. How long is the whale?