A man rows to a place 24 km distance and come back in 7 hours. He finds that he can row 2 km with the up stream in the same time as 3 km against the down stream. The rate of the stream is Choices: A) 10/3 km/hr B) 13/3 km/hr C) 20/7 km/hr D) 30/7 km/hr E) 40/7 km/hr
Explanation:   Speed down stream = distance/time = 3/x   Speed up stream = distance/time = 2/x   Time taken to row 24 km up stream and down stream is   = 48/(2/x) + 48/(3/x)   = 48x/2 + 48x/3 = 48x(5/6) = 8x+5 = 40x   40x = 7   x = 7/40 hr   Speed of down stream 3/(7/40) = 120/7   speed of up stream = 2/(7/40) = 80/7   Rate of stream = 1/2(a - b) = 1/2[(120/7)-(80/7)]   = 1/2(40/7)   = 20/7 km/hr   Answer: Option 20/7 km/hr
<result>C</result>
A man rows to a place 24 km distance and come back in 7 hours. He finds that he can row 2 km with the up stream in the same time as 3 km against the down stream. The rate of the stream is