Question

a car moves 30 minute with uniform speed of 30 kilometre per hour and next 30 minute moves with a uniform speed of 60 km per hour find the average speed in entire journey
Ans Total diatance 60+30=90km
TIME=2HOURS
AVERAGE SPEED TOTAL DISTANCE/TOTAL TIME
90÷2=45KM/H
IS IT CORRECT

Answer 1

Now your answer is wrong.
Because Average speed = total distance /total time
Here total time = 30 min + 30 min = 60 min = 1 h
Total distance was not given in the question.

For 1st 30 min
The speed of car = 30 km/h
For 1 h the car moves a distance of 30 km
For 30 min(1/2 h)  the distance traveled by car = 30 * 1/2 = 15 km

For next 30 min
The speed of car = 60 km/h
For 1 h the car moves a distance of 60 km
For 30 min (1/2 h) the distance moved by car = 60*1/2 = 30 km

Total distance = 15 + 30 = 45 km

Average speed = total distance/total time
                           = (15 + 30)/1
                           = 45 km/h is the right answer. 

Answer 2

Answer:total time 30+30=60min=1hour

For1st 30 min

=30 min(1/2)

=15km

For 2nd 30 min

=60min(1/2)

=30km

Average speed=45/1

=45km/h

Explanation: