A wave has a wavelength of 3 mm and a frequency of 4 Hz. At what speed does the wave travel?

The relationship between the wavelength, frequency and
speed of a wave is c = L*F, where c is the wave velocity, L is the wavelength and F is
the frequency.

Here the wavelength is given as 3 mm and the
frequency is 4 Hz or 4 per second, this gives the wave velocity
as

c = 3*10^-3*4 = 12*10^-3
m/s.

The given information can be interpreted as 4 waves
with a wavelength of 3 mm can pass in a second.

We see from
the equation given earlier that for a constant velocity, waves with a higher wavelength
have a lower frequency and those with a higher frequency have a smaller
wavelength.