Aptitude - Races and Games - Discussion
Discussion Forum : Races and Games - General Questions (Q.No. 2)
2.
A and B take part in 100 m race. A runs at 5 kmph. A gives B a start of 8 m and still beats him by 8 seconds. The speed of B is:
Answer: Option
Explanation:
| A's speed = |  |
5 x | 5 |  m/sec |
= | 25 | m/sec. |
| 18 | 18 |
| Time taken by A to cover 100 m = | |
100 x | 18 | sec |
= 72 sec. |
| 25 |
Time taken by B to cover 92 m = (72 + 8) = 80 sec.
| B's speed = |
|
92 | x | 18 | kmph |
= 4.14 kmph. |
| 80 | 5 |
Discussion:
29 comments Page 2 of 3.
Manisha said:
9 years ago
I can't understand why we have to use 18/5, where it come from? Can anyone explain?
Vinay said:
10 years ago
We have given speed of A = 5 km/h => 5x5/18 = (25/18) speed;
A takes time = 100x (18/25), Time = Distance/Speed;
=72 sec;
Since A beat B by 8 sec.
So total time taken by B = 72+8 = 80 (time);
Since A gives 8 m to B.
So total distance cover by B = 100-8 = 92 (dist);
We know that Speed = Distance/Time;
Now speed of B = 92/80 m/s;
Now converting it into km/h => (92/80) x (18/5).
=> 4.4 answer.
A takes time = 100x (18/25), Time = Distance/Speed;
=72 sec;
Since A beat B by 8 sec.
So total time taken by B = 72+8 = 80 (time);
Since A gives 8 m to B.
So total distance cover by B = 100-8 = 92 (dist);
We know that Speed = Distance/Time;
Now speed of B = 92/80 m/s;
Now converting it into km/h => (92/80) x (18/5).
=> 4.4 answer.
Deepali said:
1 decade ago
How get 18?
Buddhika said:
1 decade ago
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.
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.
(2)
Prasanna said:
1 decade ago
Why can't we change the distance into km and solve?. I am not getting the answer in that way.
(1)
Girijesh said:
1 decade ago
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.
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.
(1)
Prafull gadekar said:
1 decade ago
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.
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.
(3)
Qwaci said:
1 decade ago
@ Sag & Mangesh.
First of all, A gave B a start of 8m so B did not run 100m but 92m (100m-8m). Secondly, A took 72sec to cover the 100m and still won B who had only 92m to run by 8sec which means that with the 92m that B covered he used or needed 80sec (72sec+8sec). I hope my little explanation could help you understand.
First of all, A gave B a start of 8m so B did not run 100m but 92m (100m-8m). Secondly, A took 72sec to cover the 100m and still won B who had only 92m to run by 8sec which means that with the 92m that B covered he used or needed 80sec (72sec+8sec). I hope my little explanation could help you understand.
(1)
Mangesh said:
1 decade ago
Since both are covering 100m finally. So why we took 92m instead 100m ?
(1)
Sag said:
1 decade ago
We are adding 8 second to cmplete 100m for b. So why his speed is calulated for 92 m. It should be for 100m and answer should be 4. 25.
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