Question

a car travels 30 km at a uniform speed of 40 km per hour and next 30 km at a uniform speed of 20 km per hour find its average speed​

Answer 1

Answer:

30 km uniform speed is (u1) = 40 km/h 

2nd 30 km uniform speed is ( u2 ) = 20 km/h

Total distance ( d )

= 30 + 30 = 60 km

Time taken in 1st time

= d / t = 30/40 also

, 3h / 4 = 180/4 = 45 min

Time taken in 2nd time

= d/t = 30/20 also,

3h/2 = 180/2 = 90 min

total time = 45 + 90 = 135 min = 135/60 h

av.speed

= 60/135/60

= 60 * 60 /135

= 26.66 km/h ( answer )  

Answer 2

for first 30km

time=30/40=3/4 of an hour =45min

for next 30km

time=30/20=3/2of an hour=1H 30MIN

total time=45min+1H 30min

=2H 15 min