Filter design, relationship between energy and stop-band ripple
$\delta_s$ is the stop-band (hence the ${}_s$ subscript) attenuation.

A signal in the stop-band with amplitude $1$ would have amplitude $\delta_s$ after filtering.

Since power goes quadratic with amplitude, and if you feed in white noise, $\frac{22}{25}$ of the original energy will be in stop band, and will be reduced by a factor of $\delta_s^2$.