How far did the person go if he/she walks 4 km north, and then walks 8 km west, and then he walks 2km north?

10km

The above graph shows the person walking. The red vector is the sum of the three blue vectors and we are looking for its magnitude. We can calculate the magnitude by drawing the dash lines, then the red line is the hypotenuse of the right triangle with one side 6 km and the other side 8 km. We can use the Pythagorean theorem to calculate the length. lenght =