The Doppler Shift - is this right?

[Shiina-kun]

Homework Statement

The Doppler shift was first tested in 1845 by the French scientist B. Ballot. He had a trumpet player sound an A 440 Hz while riding on a flatcar pulled by a locomotive. At the same time, a stationary trumpeter played the same note. Ballot heard 3.0 beats per second. How fast was the train moving toward him?

Homework Equations

f' = f/(1-Vs/V)

The Attempt at a Solution

Since it said that Ballot heard 3 bps, I added 3 to 440

443 = 440/(1-Vs/V)
>> 1-Vs/V = 440/443
>> Vs = (440/443 - 1)-V
>> Vs = (440/443 - 1)-343
>> Vs = 2.32 m/s

This doesn't seem right to me. I wasn't really sure if I should have added 3 to 440, but I didn't know how else to find the answer.

 

[Kurdt]

It seems ok. The beat frequency is of course given by $f_b = |f_2 - f_1|$.