You run for 100 seconds at a speed of 5.0 m/s and then you walk for 100 seconds at a speed of 1.0 m/s. What is your average speed?

In the first 100 sec you cover 500 m. In the second 100 sec you cover 100 m.

Therefore, you cover 600 m in 200 sec for an average speed of (600/200) m/s or 3 m/s