The intensity of a wave is proportional to the square of its amplitude. Therefore, we can calculate the ratio of intensities A/B by squaring the ratio of amplitudes A/B.
Let's denote the amplitude of the first wave as A₁ = 20 mm and the amplitude of the second wave as A₂ = 5 mm.
The ratio of amplitudes A/B can be written as A₁/A₂ = 20 mm / 5 mm = 4.
To calculate the ratio of intensities, we square the ratio of amplitudes: (A₁/A₂)² = 4² = 16.
Therefore, A/B = 16.
So, the ratio of the intensities A/B is 16.