Then 100/a=60/b and a/b= 100/60 are obtained.

Suppose the fast runner takes X steps and catches up with the slow runner, which proves that they walk the same distance. At this point, the jogger actually took X steps, so the jogger's journey after the fast runner left is x- 100, and the journey time after the fast runner left is equal.

Then x/a=(x- 100)/b, x=250.

So the fast runner has to walk 250 steps to catch up with the slow runner.