A source of sound of frequency n and a listener approach each other with a velocity equal to 1/20 of velocity of sound. What must have been the apparent frequency heard by the listener?

According to Doppler effect we have,n′=v+v0v−vsnv is speed of sound,vs is speed of source,vo is speed of observer,n is natural frequency of source and n' is observed frequency.as given, vs=vo=v20⇒n′=v+v20v−v20n⇒n′=2120v1920v=2119nThe apparent frequency heard by the listener is 2119n.