The number of wavelengths:

$\overline{){\mathbf{\#}}{\mathbf{w}}{\mathbf{a}}{\mathbf{v}}{\mathbf{e}}{\mathbf{l}}{\mathbf{e}}{\mathbf{n}}{\mathbf{g}}{\mathbf{t}}{\mathbf{h}}{\mathbf{=}}\frac{\mathbf{D}\mathbf{i}\mathbf{s}\mathbf{t}\mathbf{a}\mathbf{n}\mathbf{c}\mathbf{e}}{\mathbf{W}\mathbf{a}\mathbf{v}\mathbf{e}\mathbf{l}\mathbf{e}\mathbf{n}\mathbf{g}\mathbf{t}\mathbf{h}}}$

There is same number of wavelengths.

Consider a slab of crown glass and a tank full of water. What is the ratio of thickness of the slab of crown glass, d_{g}, to the depth of water, d_{w}, that contains the same number of wavelengths of the monochromatic lighting passing from one substance to another?