Question

John is covering 1/4th distance of total in 40 km/hr speed and remaining with 20km/hr speed calculate average speed of John

Answer 1

Explanation :

John is covering ¼ th distance of total in 40 km/h .

He is covering remaining distance with 20 km/h speed.

What is average speed of John?

Let the total distance be d km.

∴ Distance in 1st way = ¼ × d = d/4 km.

∴ Distance in 2nd way = d - d/4 = (4d - d)/4 = 3d/4 km.

We know that,

Speed = Distance/Time

⇒ 40 = (d/4)/Time

⇒ 40 × Time = d/4

⇒ Time = (d/4)/40

⇒ Time = d/160 h

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Again,

⇒ 20 = (3d/4)/Time

⇒ 20 × Time = 3d/4

⇒ Time = (3d/4)/20

⇒ Time = 3d/80 h

Now we know that,

Av. speed = Total distance/Total time

⇒ Av. speed = d/[(d/160) + (3d/80)]

⇒ Av. speed = d/[(d + 6d)/160]

⇒ Av. speed = d/(7d/160)

⇒ Av. speed = d × (160)/7d

⇒ Av. speed = 160/7

⇒ Av. speed = 22.86 km/h

∴ Average speed of John = 22.86 km/h

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Answer 2

$\bigstar$ Question

John is covering 1/4th distance of total in 40 km/hr speed and remaining with 20 km/hr speed calculate average speed of John

$\bigstar$ Answer

Let the total distance be x.

John is covering 1/4th distance of total in 40 km/hr speed

So , he covers (1/4)x distance with 40 km/h.

$\bigstar$ Case 1 : -  

Distance = x/4 m

Speed = 40 km/h

=> Time = Distance / Speed

Time = (x/4)/40 =  x/160

$\bigstar$ Case 2 : -

Distance = x-(x/4) = 3x/4

Speed = 20 km/h

Time = (3x/4)/20

=> Time = 3x/80

Now  " The average speed of an object is the total distance traveled by the object divided by the elapsed time to cover that distance."

So ,

Average Speed = (Total Distance ) / ( Total Time )

Average Speed = (x/4 + 3x/4)/(x/160+3x/80)

=> Average Speed = x / (7x/160)

=> Average Speed = 160/7 = 22.86 km / h

$\bold{\bf{\blue{Average\;Speed=22.86\;km/h}}}$