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.
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