A bus is travelling the first one-third distance at a speed of 10 km/h

1.	A bus is travelling the first one-third distance at a speed of 10 km/h, the next one-fourth at 20 km/h and the remaining at 40 km/h. What is the average speed of the bus? A. 17 km/h B. 17.8 km/h C. 18 km/h D. 20 km/h
Answer» Let the total distance be 100 km One third of 100 km = 33.33 km time = t₁ =\(\frac{33.33}{10}\) = 3.33 hr Distance left = 100 km – 33.33 km = 66.67 km One fourth of 66.67 km = 16.67 km t₂ =\(\frac{16.67}{20}\) = 0.83 hr Remaining distance = 100 km – 33.33 km – 16.67 km = 50 km t₃ = \(\frac{50}{40}\)= 1.25 hr t₁+t₂+t₃ = 5.41 hr Average speed = \(\frac{total\,distance\,travelled}{total\,time\,taken}\)= \(\frac{100}{5.41}\)= 18.4 km/hr

A bus is travelling the first one-third distance at a speed of 10 km/h, the next one-fourth at 20 km/h and the remaining at 40 km/h. What is the average speed of the bus? A. 17 km/h B. 17.8 km/h C. 18 km/h D. 20 km/h

Answer»

Let the total distance be 100 km

One third of 100 km = 33.33 km

time = t₁ =\(\frac{33.33}{10}\) = 3.33 hr

Distance left = 100 km – 33.33 km = 66.67 km

One fourth of 66.67 km = 16.67 km

t₂ =\(\frac{16.67}{20}\) = 0.83 hr

Remaining distance = 100 km – 33.33 km – 16.67 km = 50 km

t₃ = \(\frac{50}{40}\)= 1.25 hr

t₁+t₂+t₃ = 5.41 hr

Average speed = \(\frac{total\,distance\,travelled}{total\,time\,taken}\)= \(\frac{100}{5.41}\)= 18.4 km/hr