A man travels the first 150 km of his journey at 80 km/hr. Due to bad weather, he travels the next 150 km at 60 km/hr. What is his average speed for these 300 km (approximately)?
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → 68.6 km/hr
Average speed = total distance ÷ total time. It is not the simple average of 80 and 60, because the man spends more time on the slower part.
Time for the first 150 km \(\displaystyle =\frac{150}{80}=\frac{15}{8}\) hr
Time for the next 150 km \(\displaystyle =\frac{150}{60}=\frac{5}{2}\) hr
Total time \(\displaystyle =\frac{15}{8}+\frac{20}{8}=\frac{35}{8}\) hr
Average speed \(\displaystyle =300\div\frac{35}{8}=\frac{2400}{35}=68.57\approx68.6\) km/hr