This lesson is on converting miles (mi) and kilometers (km).   1 km = 0.609 mile (3 decimals).  Thus 1 mile = 1 / 0.609 which equals 1.64 km.  Dividing 1 by 0.609 equals 1.64 km.

1 km = 0.609 mi.

1 mi = 1.64 km.