Radio waves travel at the speed of light-300,000km/s.  What is the
wavelength of radio waves received at 100.1 MHz on you FM radio dial?

If 300 km/s, 2.997... metres. Speed isn?t exactly 300,000 km/s of
course, 299,792,458 m/s being commonly accepted. Therefore, 2.9949...
metres.

May be superfluous information for your requirements, but any
modulated wave consists of other frequencies as well so the 100.1 MHz
is only the mid frequency.

Best

Use this formula v = fL
where v = velocity of wave, f = frequency of wave and L = wavelength of wave.

Using your data,
300 000 000 m/s = 100.1 x 1 000 000 Hz x L
L = 2.997 m

Well, technically the speed 299,792,458 m/s is speed of light in a
vacuum. In the atmosphere of earth the index of refraction is 1.0029
which means that the actual speed for a radio wave in our atmosphere
is (approximately) v= 298,925,573.84 m/s. The wavelength would be
(using pkuanko's formula)

L=v/f = (298, 925, 573.84 m/s)/(100.1 x 1,000,000 Hz) = 2.98627 m

not much of a difference from the above calculations, but I wanted to
make sure to distiguish between a vacuum (out in empty space) and the
Earth's atmosphere (air).