Question

a man travels with a speed of 20 km/hr and then returns with a speed of 30km/hr, the average speed of the whole journey is
25km/hr
15km/hr
24km/hr
30km/hr

Answer 1

Answer:

Let the distance between A andB be the LCM of 20 and 30 which is 6Okm.

So, time taken in going from A to B= 60/20 = 3 hrs.

Time taken in coming back from B to A = 60/30 =2 hrs.

Now,

Average speed = Total Distance/Total time taken (60+60)/(3+2) = 120/5 24kmph.

Explanation:

$Hope \: it \: helps.$

Answer 2

Given

• Man's speed's = 20km/hr and 30km/hr

To find

• Man's average speed

Solution

☯ Let us consider 2 cases, one with speed 20 and another with speed 30, we can the time by taking the distance to be x. We know that distance = speed/time or time = distance/speed, let's do it.

• d = x km
• s = 20 km/hr
• T = d/s = x/20 hrs

☯ The time for first case is x/20 hrs

• d = x km
• s = 30 km/hr
• T = d/s = x/30 hrs

☯ The time for second case is x/30 hrs

☯ Now we have the time for both first and second case, we can find the average speed by using the formula, average speed = total distance/total time, let's do it,

• A.S = T.D/T.T = x+x/x/20+x/30
• A.S = 2x/3x+2x/60
• A.S = 2x/5x/60
• A.S = 2x/1×60/5x
• A.S = 120/5
• A.S = 24

☯ Hence, the average speed of the man in his whole journey is 24 km/hr