Question

If a car travels first 40 km at speed of 20 km/h and next 80 km at a speed of 40 km/h. What is the average speed of car during journey?

Answer 1

avg speed= total distance traveled / total time taken
total distance traveled according  to ques.=40+80=120km
given v1=20 kmph
          v2=40kmph
avg speed= total distance /total time
avg speed= total distance/[distance/ v1+distance / v2]
since time =distance/speed
avg speed= 120/[40/20+80/40]
                 =120/20+20
                 =120/40
                 =30 kmph