A man rows 3/4 of a km against the stream in 11x1/4 minutes and returns in 7x1/2 min

Question

A man rows \(\frac34\) of a km against the stream in \(11\frac14\) minutes and returns in \(7\frac12\) min. Find the speed of the man in still water. 

(a) 4 km/hr 

(b) 3 km/hr 

(c) 5 km/hr 

(d) 6 km/hr

Answer 1

(c) 5 km/hr

Distance covered upstream in \(\frac{45}{4}\) min = \(\frac34\) km

∴ Speed of man upstream = \(\big(\frac34\times\frac{4}{45}\times60\big)\) km/hr = 4 km/hr 

Distance covered down stream in \(\frac{15}{2}\) min = \(\frac34\) km

∴ Speed of man down stream = \(\big(\frac34\times\frac{2}{15}\times60\big)\) km/hr = 6 km/hr

∴ Speed of man in still water = \(\frac12\) (6 + 4) km/hr = 5 km/hr.