Question

A motorcyclist drives from place A to B with a uniform speed of 30 km /h and returns from B to A with uniform speed of 20 km /h. Find his average speed

Answer 1

Hey freind here is your answer

Case 1 =
Let distance by s
Speed = 30km/hr
Time = ?
Speed = Distance / Time
30 = s / Time
Time = s / 30 hr

Case 2 =
Distance = s ( as he is returning from path he has came )
Speed = 20km/hr
Time = ?
Speed = Distance / Time
20 = s / Time
Time = s / 20

Average speed = Total distance / Total time
Total Distance = s + s
= 2s
Total Time = s / 30 + s / 20 ( L.C.M = 60 )
= s / 30 * 2 / 2 + s / 20 * 3 / 3
= 2s / 60 + 3s / 60
= 3s +2s / 60
= 5s / 60
= s / 12
Average speed = 2s ÷ s / 12
= 2s * 12 / s
= 24 km / hr

Hope it helps

Answer 2

Answer:

• 24 Km/h is the average speed.

Explanation:

Given:

• A motorcyclist drives from A to B with a uniform speed of 30 Km/h and returns with a speed of 20 Km/h.

To find:

• Average speed of the motorcyclist.

Solution:

Let the distance between A and B be D.

Now,

Time taken by the motorcyclist with speed of 30 Km/h :-

⇒ Time = Distance/Speed

• D/30 hr

Time taken by the motorcyclist with speed of 20 Km/h :-

• D/20 hr

Now,

Average speed of the motorcyclist is :-

⇒ Avg. speed = Total distance/Total time

• (D + D )/(D/30 + D/20)
• (2D)/[(D(2) + D(3)/60]
• (2D)/[5D/60]
• (2D)/12D
• 12 × 2
• 24

∴ The average speed of the motorcyclist is 24 Km/h.