Answer:
25 km/hr
Explanation:
Since Ali's average speed for his trip to school is u = 20 km/hr and his average speed for the return trip to back home from school is v = 30 km/hr, thus his total average speed for the journey is thus V = (initial average speed + final average speed)/2 = (u + v)/2
Substituting the values of the variables into the equation, we have
V = (u + v)/2
V = (20 km/hr + 30 km/hr)/2
V = 50 km/hr/2
V = 25 km/hr
So, the average speed for Ali's trip is 25 km/hr