A metal \( \mathrm{M} \) crystallizes into two lattices: face centred cubic \( (\mathrm{fcc}) \) and body centred cubic \( (\mathrm{bcc}) \) with unit cell edge length of \( 2.0 \) and 2.5 Å respectively. The ratio of densities of lattices fcc to bcc for the metal \( \mathrm{M} \) is ______. \([\text{Nearest integer}]\)
