Question

abdyl while runing to school ,computers the average speed for his trip to be 20 kmh-1 on his return trip along the same route there is less traffic and the average speed is 30kmh-1 what is the averge speed for abdul trip 

Answer 1

Let distance between home to school = x km
average speed while going = 20 km/h
time taken (t₁) = (x/20) h
average speed while returning = 30 km/h
time taken (t₂) = (x/30) h
total distance = x+x = 2x
total time = (x/20) + (x/30) = x(1/20 + 1/30) = x[(3+2)/60] = x(5/60) = x/12 h

Average speed = total distance/ total time taken
                       =2x/(x/12)
                       =(2x/x)×12
                       = 24 km/h

Answer 2

so let the distance to school be x 
so time taken to go school = x/20 hr
and time taken to return home = x/30 

total time = x/20 + x/30 = x/12
so total distance = x + x = 2x 

so average speed = 2x / x/12 = 2 x 12 = 24 km/h