1.  A man travelled from the village to the post-office at the rate of 25 kmph and walked back at the rate of 4 kmph. If the whole journey took 5 hours 48 minutes, find the distance of the post-office from the village.
A. 40 km
B. 20 km
C. 60 km
D. None of these

Answer: Option B

Explanation:

Average speed = (2xy / x + y) km/hr
        = (2 x 25 x 4 / 25 + 4) km/hr
        = 200 / 29 km/hr

Distance travelled in 5 hours 48 minutes
i.e, 5 x (4 / 5) hrs = (200 /29 x 29 / 5) km = 40 km

∴ Distance of the post office from the village = (40 / 2) = 20 km