Question

: - A marathon runner covers half of the 24 kilometers at a speed of 18 km/hr then runner
increases speed by 6 km/hr to complete the marathon. What is his average speed of
marathon?


please help ​

Answer 1

Given :

• A marathon runner covers half of the 24 kilometers at a speed of 18 km/hr.

• Then runner increases speed by 6 km/hr to complete the marathon.

To find :

• Average speed of marathon = ?

Step-by-step explanation :

1st Case :

A marathon runner covers half of the 24 kilometers at a speed of 18 km/hr .

Given :

• Distance = 12 km

• Speed = 18 km/hr

• Time =?

We know that,

Time = Distance / Speed

Substituting the values in the above formula, we get,

= 12/18

= 2/3.

Therefore, Time = 2/3 hour.

2nd Case :

Runner increases speed by 6 km/hr to complete the marathon.

Given :

• Distance = 12 km

• Speed = 24 km/hr

• Time =?

As we know that,

Time = Distance / Speed

Substituting the values in the above formula, we get,

= 12/24

= 1/2.

Therefore, Time = 1/2 hours.

Now,

Total time = 2/3 + 1/2 =4 + 3/6= 7/6 hours.

Total Distance = 24 km [Given]

We know that,

Average speed = Total Distance / Total Time

Substituting the values in the above formula, we get,

= 24/(7/6)

= 24 × 6/7

= 144/7

= 20.58.

Therefore, Average speed of marathon = 20.58 km/hr¯¹

Answer 2

_______________________________

✰Question✰

❍ A marathon runner covers half of the 24 kilometers at a speed of 18 km/hr then runner

increases speed by 6 km/hr to complete the marathon. What is his average speed of

marathon?

_______________________________

✰Given :-

⋄ Total distance covered by runner =24 km.

⋄ He covered half of 24km at speed of 18km/h

∴ Half of 24/2=12km

⋄Next distance covered by runner at speed = 18km/h +6km/h=24km/h

_______________________________

✰ To Find:-

Average speed of runner.

_______________________________

✰Solution :-

Time taken by runner in First case.

Time = Distance /speed

t= 12/18

t= 2/3s

and, Now in second case

t'=d/s

t'= 12/24

t'=1/2

∴ Total time taken by runner =t+t'=2/3+1/2= 7/6s

Average speed=Total distance /total time taken

Av. Speed=24 × 6/7=144/7=20.57m/s

Av. speed =20.57m/s

∴The average speed of runner is 20.57m/s.