SOLUTION: A boy can row a boat at a constant rate of 7 mi/hr in still water, as indicated in the figure. He rows up-stream for 18 minutes and then rows downstream, returning to his starting

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Question 342770: A boy can row a boat at a constant rate of 7 mi/hr in still water, as indicated in the figure. He rows up-stream for 18 minutes and then rows downstream, returning to his starting point in another 16 minutes. Find the rate of the current
Answer by mananth(16946) About Me  (Show Source):
You can put this solution on YOUR website!
let rate of current be x mph
still water speed = 7mph
..
upstream speed = 7-x mph
down stream speed = 7+x mph
...
time upstream = 18 minutes = 18/60 = 3/10 hours
downstream speed = 16 minutes = 16/60 = 4/15 hours
..
Distance = time * speed
distance upstream = (7-x)*3/10 miles
distance downstream = (7+x)*4/15 miles
..
But distance is same
(7-x)*3/10 = (7+x)*4/15 miles
(7-x)*3*15=(7+x)*4*10
315-45x=280+40x
315-80=40x+45x
35=85x
x=35/85
speed of current = 0.411 mph
..