If A runs 3 times as fast as B and A gives B a start of 60 m, then how far must be winning post on tracks so that A and B reach at same time?

90 m

$\text{Let speed of B}=v.$

$\text{Speed of A}=3v.$

$\text{Let distance of race}=D.$

$\text{B runs }D-60\text{ metres, A runs }D\text{ metres}.$

$\text{Equal time condition:}$

$\frac{D}{3v}=\frac{D-60}{v}.$

$D=3(D-60).$

$D=3D-180.$

$2D=180.$

$D=90.$

$\text{Winning post must be }90\text{ m away.}$