1. The problem statement, all variables and given/known data Mary is blowing her trombone at 400hz. Paul is approaching her at speed v, blowing the same type of trombone. These trombones has a maximum frequency of 500hz. What is the maximum speed Paul can approach Mary, and still cancel out her trombone noise? 2. Relevant equations f = f0/(1-vs/v) Speed of sound = 340m/s 3. The attempt at a solution Max freq 500, so: 500 = 400/(1-v/340) Solving for v, I get 68 m/s. The answer is 85 m/s. What's going on?