If the two speeds are for equal distances, use the harmonic mean: Average speed = 2ab / (a + b)
If the two speeds are for equal time periods, use the arithmetic mean: Average speed = (a + b) / 2
If the distances or times are not equal, use: Average speed = Total distance / Total time
Let a and b be the two speeds
Determine whether the distances traveled at each speed are equal
Determine whether the time spent at each speed is equal
Apply the appropriate formula based on the situation
Keep units consistent when calculating the result