In a race of 200 metres, B can give a start of 10 metres to A and C can give a start of 20 metres to B. The start that C can give to A, in same race, is :

$$\eqalign{ & \,\,{\text{A}}\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,{\text{B}}\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,{\text{C}} \cr & 190\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,200 \cr & 180\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,200 \cr & \,\,{\text{A}}\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,{\text{B}}\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,{\text{C}} \cr & 171\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,180\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,200 \cr} $$

⇒ C can give a start of 200 - 171 = 29 metres to A