If A : B = 7 : 9 and B : C = 5 : 4, then A : B : C is -

$$\eqalign{ & = {\text{A}}:{\text{B}} = 7:9\,{\text{and}} \cr & {\text{B}}:{\text{C}} = 5:4 \cr & = \left( {5 \times \frac{9}{5}} \right):\left( {4 \times \frac{9}{5}} \right) \cr & = 9:\frac{{36}}{5}. \cr & \Rightarrow {\text{A}}:{\text{B}}:{\text{C}} = 7:9:\frac{{36}}{5} \cr & \,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\, = 35:45:36. \cr} $$