| A and B run a race of 1 km. A gives a start of 50 m and still beats him by 15 s. If A runs at 8 km/h, what is the speed of B? |
A) 4.4 km/h
B) 5.4 km/h
C) 6.4 km/h
D) 7.4 km/h
Correct Answer: D
Solution :
| Total distance = 1000 m |
| Speed of \[A=8\,km/h\,\,=\,\,8\times \frac{5}{18}=\frac{20}{9}\,\,m/s\] |
| Time taken by A to cover this distance |
| \[=\,\,\frac{1000\times 9}{20}=450\,s\] |
| Now, time taken by B to cover 950 m, |
| Total time \[=450+15=465\text{ }s\] |
| \[\therefore \] Speed |
| \[=\,\,\frac{950}{450+15}=\,\,\frac{950}{465}\times \frac{18}{5}=7.3548\approx 7.4\,km/h\] |
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