Use total distance and average speed to find total time, then find walking time and speed.<br><br>
&bull; Time for running = 600 ÷ 3 = 200 s<br>
&bull; Total distance = 600 + 400 = 1000 m<br>
&bull; Average speed 1 m/s → total time = 1000 ÷ 1 = 1000 s<br>
&bull; Walking time = 1000 − 200 = 800 s<br>
&bull; Walking speed = 400 ÷ 800 = 0.5 m/s<br><br>
Final Answer: 0.5 m/s