Practicing Success
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) |
51.25 km/h 45.75 km/h 58.25 km/h 49.77 km/h |
49.77 km/h |
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) |