Question

a car travels from a to b at a speed of 20 km per hour and returns with a speed of 30 kilometre per hour what is the average speed of the car?

Answer 1

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Distance between a to b=20km
then returned b to a=30km

average speed =Total distance /total time taken

average speed=> 20km+30km/2hour
➡50km/2hour
➡25km/h

Answer 2

let a - b distance be d
for 1st trip,
speed = distance/time
20 = d/t1
hence, t1 = d/20

for 2nd trip,
speed = distance/time
30 = d/t2
hence, t2 = d/30

total time = t1 + t2
= d/20 + d/30
= d (1/20 + 1/30) [took d common]
= d (20 + 30/20*30)
= d (50/600)
= d (1/12)

speed average = total distance/total time
= 2d/ [d(1/12)]
= 2/ (1/12)
= 24 km/hr

Hence, average speed of the car will be 24 km/hr.

Hope it helped☺️☺️