RRB Non Technical Model Papers 10 with solutions

Let $1/3=x.1/4=y,1/5=z.$
So,
${x^3+y^3+z ^3-3xyz}/{x^2+ y^2+ z^2- xy- yz -xz}$
$={(x+y+ z)(x^2 +y^2 +z^2- xy -yz -xz)}/{x^2+ y^2+ z^2- xy -yz- xz}$
$=x +y+ z=1/3 +1/4 +1/5 =47/60$