| A man travels a distance of 24 km at 6 km/h another distance of 24 km, at 8 km/h and a third distance of 24 km at 12 km/h. His average speed for the whole journey (in km/h), is [SSC (CPO) 2008] |
A) \[8\frac{2}{3}\]
B) 8
C) \[2\frac{10}{13}\]
D) 9
Correct Answer: B
Solution :
| Average speed \[=\frac{3xyz}{xy+yz+zx}\] |
| \[=\frac{3\times 6\times 8\times 12}{6\times 8+8\times 12+6\times 12}\] |
| \[=\frac{3\times 6\times 8\times 12}{48+96+72}\] |
| \[=\frac{3\times 6\times 8\times 12}{216}=8\,km/h\] |
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