Geo has been driving his four-wheel drive with great difficulty in the desert since dawn. At the moment, he is at a distance of 100 kilometres from Mathstown and 120 kilometres from Computown. He knows that these two towns are linked by a 100 - kilometre track. This track is straight and suitable for motor vehicles.
What distance must Geo cover to reach that track ?
D’après le Rallye Poitou Charente 1995