A man goes downstream with a boat to some destination and returns upstream to his original place in 4 hours 54 minutes. If the speed of the boat in still water and the stream are 31.85 km/hr and 13.65 km/hr respectively, the distance of the destination from the starting place is?
Answer & explanation
Correct answer: option 2
Downstream speed = 31.85 + 13.65 = 45.5
Upstream speed = 31.85 - 13.65 = 18.2
Distance = \(\frac{Product\;of\;speeds}{sum\;of\;speeds}\) × Time (shortcut)
= \(\frac{45.5\;×\;18.2}{45.5\;+\;18.2}\) × 4\(\frac{54}{60}\)
= \(\frac{828.1}{63.7}\) × \(\frac{49}{10}\)
= 63.7 km