Aptitude - Races and Games - Discussion

@Ramanjaneyulu.


Multiplying by 5/18, you can convert km/h to m/s.

Actually, B has to complete 92 meters in 72 seconds but he is taking an extra 8 seconds time to complete 100 meters which can be concluded from the question. Am I right?

Instead of taking 5/18, we solve like,

A 's speed = 5 kmph = 5000 mph = 5000/3600 = 1.38m/sec,

For 100m distance time = 72.3 sec or 72 sec,

B's require time to cover 92m distance=(72+8) = 80 sec.

80 sec- 92m then,

1 sec - 1.15m.

1.15m/sec.

1.15*3600 = 4140 mph = 4.14 kmph.

How 5/8 came? please explain me.

Forget 5 kmh.

A runs = 8 m.
B runs = 100-8 = 92 m.
B speed = 92 m/8 s = 11.5 ms.

Now we convert ms = kmh.

11.5 x 18/5 = 4.14 kmh.

That is all.

Why can't we change the distance into km and solve?. I am not getting the answer in that way.

Here A runs for 100meters while B has to run only for 92Meters as B is 8meters ahead of A.

5km per hour=5000 meters per hour.

As the question is asking in seconds. Now convert for each second how many meters A is running.

Here we have 3600 seconds for one hour.

So 5000meters or 5*1000meters/3600 which comes to 5*5/18=25/18.

In how many seconds A ran the100meters =100m*25/18sec=72sec.

A has run 8seconds faster than B. Which means B took 8seconds more to complete the run. Therefore 72+8=80Sec.

Now the question is B's speed in km per hour.

Calculate for each sec how many meters he ran=92meters/80sec.

Hence=92/80*18/5 (lets say 3600sec/1000meters) =4.14kmph.

How come 5/18? Please tell me.

How get 18 came here?

Let speed of B is x meter/sec.

Speed of A is y meter/sec.

Total time to reach 100 meter by A is 100m/5kmph = 72 sec.

Total time to reach 100 meter by B is:

(8/x) + time taken by A + 8 = 100/x.

(8/x) + 72 + 8 = 100/x.

x = 92/80 m/s = 4.14 kmph.