Here the tortoise has a head start but its speed is lesser than his competitor
T: tortoise
R: rabbit
Now to win rabbit has to cross tortoise: i.e. it has to come to the position of tortoise and then go ahead: look at the figure below: rabbit has to go first point B where the rabbit is and then go ahead. But by the time rabbit reach B tortoise moved to C: now the whole thing can be seen fresh: R has to come to the position of tortoise and then go ahead : i.e. rabitt has to go C and then ahead but by the time it reaches C tortoise move to D ::::: So tortoise will be always ahead of the rabbit :::::: but as we know if the distances are sufficiently large rabbit must win:::: what is wrong with logic
R________T_____________
A________B_____________


_________R_____T________
A________B_____C_______


________________R__T____
A________B_____C__D____