A man covers half part of a certain distance at 25 km/hr. He covers 40 percent of remaining distance at the speed of 8 km/hr and covers rest of the distance at the speed of 18 km/hr. What is his average speed for the entire journey?
(600/37) km/hr
Given data:
Half the distance at a speed of 25 km/hour,
40% of the remaining distance at a speed of 8 km/hour,
For the remaining distance at a speed of 18 km/hour;
Concept:
Use the formula for average speed = \(\rm \frac{total\ distance}{total \ time}\)
Solution:
Let the total distance be 2D.
⇒ Time for half the distance = \(\rm \frac{D}{25}\)
⇒ Time for 40% of the remaining distance = \(\rm \frac{0.4\ D}{8}\)
⇒ Time for the remaining distance = \(\rm \frac{0.6\ D}{18}\)
⇒ Total time = \(\rm \frac{D}{25}+\frac{0.4D}{8}+\frac{0.6D}{18}=\frac{37D}{300}\)
⇒ Average speed = \(\rm \frac{2D}{37D/300}=\frac{600}{37}\) km/hour
Thus, the required average speed \(\frac{600}{37}\) km/hour is.
Important Questions from Speed Time and Distance
A journey of 900 km is completed in 11 h. If two-fifth of the journey is completed at the speed of 60 km/h, at what speed (in km/h) is the remaining journey completed?
A car starts from point A towards point B, travelling at the speed of 20 km/h. 1 \(\frac{1}{2}\) hours later, another car starts from point A and travelling at the speed of 30 km/h and reaches 2 \(\frac{1}{2}\) hours before the first car. Find the distance between A and B.
A bus covered a distance of 162 km. If speed of this bus is 15 m/s, then what will be the time taken ?
An athlete runs an 800 m race in 96 seconds. His speed (in km / h) is:
A person has to cover a distance of 150 km in 15 hours. If he traveled with the speed of 11.8 km/hr for 10 hours. At what speed he has to travel to cover the remaining distance in the remaining time?
