A person walks on a plain land at 4 km/hr. and up the slope at 3 km/hr. and comes down at 6 km/hr. and walks on the plain land again at 4 km/hr. if he started at 3:00 pm and comes back at 9:00 pm. What is the one-way distance?
24 km
12 km
10 km
None of these
Explanation:
Given, his speed on plain and upward was 3km/hr. and 4 km/hr.
Average speed a = 24/7.
When he was coming back his speed was 6km/hr. and 4 km/hr.
Average = b = 24/5.
So Overall average speed v = 4 km/hr.
Given, time = 6hr (i.e. from 3pm to 9 pm)
Now, v = d/t
=> d=v $\times$ t
=> d=4 $\times$ 6=24km (two-way distance)
Therefore, one-way distance = 12 km.