Frequency of two objects moving toward eachother

[eagles12]

Homework Statement

A motorcyclist and a police car are moving toward one another. The police car emits a sound with frequency of 502 Hz and has a speed of 27m/s. The motorcycle has a speed of 12 m/s.
What frequency does the motorcyclist hear?

Homework Equations

f=1/T
f'=f(1+v/vs)

The Attempt at a Solution

f'=502(1+27/12)
This gave me f'=1631.5 but it says this is incorrect

 

[MrWarlock616]

I think your equations are wrong. According to the Doppler Effect, the apparent frequency $n_a=(\frac{V+V_o}{V-V_s}) n$

$V$ is the velocity of sound.

 

[eagles12]

so it would be
(27+343)/(12-343)*502
f=-561.15

 

[MrWarlock616]

read my post again.