Question

Abdul while driving to school gets speed 20km/hr on his return trip along the same road there is less traffic and average speed is 30km/hr . what is the average speed of Abdul's trip .

Answer 1

Strategy: We need to calculate the time taken in each of the trip. After that, we can calculate the average speed.

Let the distance of the school = s km

Let time to reach the school in first trip = t1

Let time to reach the school in second trip = t2

We know that average speed =Total distancetime taken=Total distancetime taken

∴ Average speed in first trip =st1=st1

⇒20 km/h=st1⇒20 km/h=st1

⇒t1=s20h⇒t1=s20h

∴ Average speed in second trip =st2=st2

⇒30 km\h=st2⇒30 km\h=st2

⇒t2=s30h⇒t2=s30h

Now total time (t1+t2)=s20+s30(t1+t2)=s20+s30

⇒(t1+t2)=3s+2s60h⇒(t1+t2)=3s+2s60h

⇒(t1+t2)=5s60h=s12h⇒(t1+t2)=5s60h=s12h

Now, Average in both of the trips =Total distance coveredTotal time taken=Total distance coveredTotal time taken

=2ss/12 km/h=2ss/12 km/h

=2s×12s km/h=24 km/h=2s×12s km/h=24 km/h

Therefore, average speed of Adbul = 24 km/h

Answer 2

Since abdul travels the same distance average speed = 2v1v2 ÷v1+v2 Here v1 equals20km per hr and v2 equals30km per hr Then average speed equals 24km per hr