If a wave has a frequency of 5.0 waves per second and the distance between the peaks of the wave is 20 cm. What is the speed of the wave?

wave velocity = frequency in Hz x wavelength in meter

So frequency = 5 Hz and wavelength = distance between successive peaks = 20 cm = 20/100 m

Hence wave velocity = 5 * 20/100 = 1 m/s