Wild Bill can shoot a pistol while riding his horse at full speed.  His horse runs at 20 feet per second, and a bullet fired from his gun flies at a speed of 400 feet per second.  But if he fires a gun while riding his horse, and the gun is aimed in the same direction that the horse is running, how much faster, in feet per second, is the bullet flying than if he fires the bullet in the opposite direction of what the horse was running?
If he fires a bullet in the same direction as the direction that the horse is running, the total speed of the bullet is the sum of the speed the bullet was propelled out of the gun plus the speed of the horse, for a combined speed of 400+20=<<400+20=420>>420 feet per second.
If he fires a bullet in the opposite direction as the direction in which the horse is running, then the total speed of the bullet is the speed the bullet was propelled out of the gun minus the speed of the horse, for a resulting speed of 400-20=<<400-20=380>>380 feet per second.
Thus, when firing the gun in the same direction as the horse is running, the bullet moves at 420-380=<<420-380=40>>40 feet per second faster than when he fires the bullet in the opposite direction as what the horse is running.
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