To calculate the average speed, you can use the formula:
\[ \text{Average Speed} = \frac{\text{Total Distance}}{\text{Total Time}} \]
In this case, Obi runs a distance of 400 meters in 40 seconds. Plugging in the values:
\[ \text{Average Speed} = \frac{400 , \text{m}}{40 , \text{s}} = 10 , \text{m/s} \]
So, Obi's average speed is 10 meters per second.