#"New unit of mass " (u_m )=20g"#

#"New unit of length " (u_l )=5cm#

#"New unit of volume " (u_v )=u_l^3=(5cm)^3=125cm^3#

#"New unit of density " u_d=(u_m/u_v )=(20g)/(125cm^3)=4/25xxg/(cm^3)#

#"So " 1g/(cm^3)=25/4 u_d#

#"So the density in new unit"#

#= 25/4xx" Value of Density in old unit"#

#=25/4xx80=500 u_d#