A) 30 km/h,
B) 20 km/h
C) 60 km/h
D) 40 km/h
Correct Answer: B
Solution :
[b] Required average speed \[=\frac{7\times 4}{\frac{7}{10}+\frac{7}{20}+\frac{7}{30}+\frac{7}{60}}\] \[\left( \therefore \text{Speed=}\frac{\text{Distance}}{\text{Time}} \right)\] \[=\frac{28\times 60}{7\times 6+7\times 3+7\times 2+7\times 1}\] \[=\frac{28\times 60}{42+21+14+7}=\frac{28\times 60}{84}=20\,km/h\] |
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