# Thread: How fast did the courier bike?

1. ## How fast did the courier bike?

Hi,

A military column of 1 km length marches with a constant speed of 6 kilometers per hour. A courier from the back of the column is sent to the head of the column by bike to deliver a message. Arrived at the front, he
instantly returns. When he returns again at the back, the column has travelled a distance of 1 km since the start of his errand. The courier drove with constant speed.

How fast did the courier bike?

Thanks

Gokulakrishnan K

2. ## Re: How fast did the courier bike?

hi,

i think it is 4km/hour

thanks
Sushma

How Sushma?

Thanks

G K

4. ## Re: How fast did the courier bike?

If i understood the question correctly..

thanks
raj

5. ## Re: How fast did the courier bike?

Is 12 Km/Hr right answer??..I am getting 12km/hr

6. ## Re: How fast did the courier bike?

Explanation: Column speed = 6 kmph (given)
Distance travelled by Column = 1 km. (given)
Let the time taken by Column to travel 1 km be ' T ' hr.
speed = distance / time ( Basic formulae )
6 = 1/T
T = 1/6 hr ( i.e 0.1666667 hr ) ---> Equation 1

It is given that during this ' T ' hr, courier travelled from back of column to front & from front to back of column. Since the Column is 1 km long, so the distance travelled by courier is 2 km.

Finally applying basic formulae of speed to courier i.e.
speed = distance travelled/ Time taken
= 2 km / 0.166666667 hr ( From equation 1 )
= 2 / 1/6
= 12 kmph --> Q.E.D

kraots & amitpatel66 you guys are right !!..

Cheers,
Anup | Mahindrakar

7. ## Re: How fast did the courier bike?

the speed of courier bike is 0.2777 km/hr

its 18 Km/hr

9. ## Re: How fast did the courier bike?

18 km/hr. Below is the solution-

1 km 0.5km 0.5km
0-------------------A--------X----------B
<=military column===>

OA represents the initial military column line. Let the courier bike meet the head at point X as shown in the above figure. Let B be the end point where the head ends exactly when the bike reaches back 0. For this reason, AX = XB = 0.5 each

Time taken by bike to travel the distance OX = Time taken by head to travel XB
Applying the formula, time = distance / speed on either sides of the above equation,

1.5 / bike_speed = 0.5 / 6
=> bike_speed = 18 km/hr

10. ## Re: How fast did the courier bike?

The answer is 14.4 km/hr.The total distance covered by column is 1 km.Time taken is 1/6 hr.Now the biker rides with speed x km/hr.Total time taken by him is 1/x-6 hr + 1/x+6 hr=1/6 hr.Solving equn u get 14.4 km/hr.Remember relative speed??

11.

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