With alloys, the formula given is akin to the 'empirical formula' for molecules, i.e. the simplest integer ratio. For the mass fraction, the relative masses of

With alloys, the formula given is akin to the 'empirical formula' for molecules, i.e. the simplest integer ratio. For the mass fraction, the relative masses of atoms of iron:neodymium:boron are approx 56:144:11, so Nd2 Fe14 B should be 27% Nd, 72% Fe and 1% B by mass, I think.