If you cover 0.5 km every minute, and keep it up for 25 minutes,
then you will cover
0.5 + 0.5 + 0.5 + 0.5 + 0.5 +
0.5 + 0.5 + 0.5 + 0.5 + 0.5 +
0.5 + 0.5 + 0.5 + 0.5 + 0.5 +
0.5 + 0.5 + 0.5 + 0.5 + 0.5 +
0.5 + 0.5 + 0.5 + 0.5 + 0.5 = 12.5 km.
An easier way to write the same thing is
(25) times (0.5 km) = 12.5 km.