A galvanometer has resistance '$\mathrm{G}' \Omega and '\mathrm{I}_{\mathrm{g}}' is current flowing through it which produces full scale deflection. '\mathrm{S}_1' is the value of shunt which converts it into an ammeter of range 0 to '3 \mathrm{I}' and '\mathrm{S}_2' is the shunt value which converts it into an ammeter of range 0 to '4 \mathrm{I}', the ratio \mathrm{S}_2: \mathrm{S}_1$ is