Question

A train travels 20 km at uniform speed of 60 km per hour and next 20 kilometres at an uniform speed of 80 kilometre per hour calculate its average speed​

Answer 1

Step-by-step explanation:

speed = dist. /time

dist. = 20 km

time = 60kmh

20km /60 kmh = 0.33 hr

next dist. = 20 km

time= 80 kmh

20km/80kmh = 0.25 hr

av. speed = total dist. /total time taken

40 km / 0.58 hrs. = 68.96 kmh

Answer 2

Answer:

Step-by-step explanation:

The distance covered by the train is 40km

at 1st 20kms the speed of the train was 60km/h

               time ( t1 ) = 20/60 h = 1/3 h

next 20kms at a speed of 80km/h

              time ( t2 ) = 20/80 h = 1/4 h

average speed = total distance covered / total time taken

                         = 40/(1/3 + 1/4)

                         = 40/{( 3 + 4 )/ 12}

                         = 40 * 12 / 7 = 68.57 km/h