20% of a journey is covered at a speed of 80 km/h, 25% of the journey at a speed of 100 km/h and the rest at 110 km/h. What is the average speed (in km/h) for the whole journey?
Answer & explanation
Correct answer: option 4
Let total distance = 100 km
Total time = \(\frac{20}{80}\) + \(\frac{25}{100}\) + \(\frac{55}{110}\)
= \(\frac{1}{4}\) + \(\frac{1}{4}\) + \(\frac{1}{2}\)
= 1
Avg. speed = \(\frac{Total\;distance}{Total\;time}\)
= \(\frac{100}{1}\)
= 100 km/h