To arrive on schedule, a train is to cover a distance of 60km at 72km/hr. If it starts 10 minutes late, at what speed must it move to arrive on schedule?
A. 60km/hr B. 80km/hr C. 90km/hr D. 108km/hr
Correct Answer: C
Explanation
\(speed = \frac{distance}{time}\\ 72 = \frac{60}{time}\\ t = \frac{60}{72} = \frac{5}{6}hr\) time lost = 10mis \(= \frac{10}{60}hr = \frac{1}{6}\) Time required for the journey \(=\frac{5}{6}-\frac{1}{6} = \frac{2}{3}\\ speed \hspace{1mm}=60 \div \frac{2}{3} = 90km/hr\)
