Two-thirds of a certain distance was covered at the speed of 45 km/h, one-fourth at the speed of 60 km/h and the rest at the speed of 75 km/h. Find the average speed per hour for the whole journey. (correct to 2 decimal places)
Answer & explanation
Correct answer: option 4
Let total distance = 1200 km
Two-thirds of Distance = 800 km
Time 1 = \(\frac{800}{45}\)\ = \(\frac{160}{9}\)\
one - fourths of Distance = 300 km
Time 2 = \(\frac{300}{60}\)\ = 5 hours
Remaining Distance = 1200 - 1100 = 100km
Time 3= \(\frac{100}{75}\)\ = \(\frac{4}{3}\)\
Total time = \(\frac{160}{9}\)\ + 5 + \(\frac{4}{3}\)\
= \(\frac{217}{9}\)\
Average speed = \(\frac{ 1200 × 9}{217}\)\
= 49.769 km/h
= 49.77 km/h ( approx)