Question

40. A train travels the first 15 km at a uniform speed of 30 km/h; the next 75 km at a uniform speed of
50 km/h; and the last 10 km at a uniform speed of 20 km/h. Calculate the average speed for the entire train
journey.​

Answer 1

$avg \: speed \: = \frac{total \: distance \: traveled}{total \: time \: taken \: }$
time taken to travel 15 km distance speed of 30km/hr = 0.5hr
75km distance speed of 50km/hr = 1.5hr
10km distance speed of 20km/hr = 0.5hr
$avg \: speed = \frac{15 + 75 + 10}{0.5 + 1.5 + 0.5} \\ = \frac{100}{2.5} \\ = \frac{40km}{hr}$