1. The problem statement, all variables and given/known data A woman is riding a bicycle at 18.0 m/s along a straight road that runs parallel to and right next to some railroad tracks. She hears the whistle of a train that is behind. The frequency emitted by the train is 840 Hz, but the frequency the woman hears is 778 Hz. Take the speed of sound to be 340 m/s. (a) What is the speed of the train? (b) What frequency is heard by a stationary observer located between the train and the bicycle? (c) Is the train traveling away from or toward the bicycle? 2. Relevant equations Moving Source frequency prime = initial frequency / 1 +/- source speed/wave speed + for receding - for approaching Moving observer frequency prime = frequency/ 1+/- observer speed/wave speed wave speed = speed of sound (343 m/s) 3. The attempt at a solution I tried setting frequency primes equal, but that didn't work out. I know you have to combne both equations because both the source and the observer are moving. The train is moving away, but I got that right on a guess so I'd like to know how to tell which way it's moving mathematically.