The relationship between the speed, frequency and wavelength is best found from a simple example.
Isobel sets up a ripple tank to produce 2 waves each second (i.e. frequency = 2 Hz). She times the waves 2 s to travel the 100 cm distance to the other side of the tank. She measures the distance between the waves as 25 cm: this is the wavelength.
A frequency of 2 Hz means one wave is produced every 0.5 s (this is known as the time period of the waves and is 1÷frequency).
In 0.5 s, waves move 25 cm, so we can find the speed using: