Boats and Streams :
Downstream : In water direction along the stream is called downstream.Upstream : In water direction against stream is called upstream.
Rule : If the speed of a boat in still water is x km/hr and the speed of the stream is y km/hr, then:
Speed downstream = ( x + y ) km/hr
Speed upstream = ( x - y ) km/hr
Rule : If the downstream speed is a km/hr and the speed upstream is b km/hr, then
Ex. A man can row a boat in upstream at 6 kmph and downstream at 12 kmph. Find the man's rate in still water and the rate of current.
Ex. A man can row 15 km /hr in still water. It takes him twice as long to row upstream as to row downstream. Find the rate of stream ?
Solution : Let man's rate in upstream be x km/hr, then his rate in downstream is = 2x kmph
So rate in down stream= 2x= 20 km/hr
Ex. A man can swim 6 km / hr in still water. If river's rate is 2 km / hr, it takes the man 3 hours to row to a place and back. How far is the place ?
Solution : Man's rate in upstream=( 6 - 2 ) km/hr = 4 km/hr
Man's stream rate in downstream= ( 6 + 2 ) km/hr = 8 km/hr
Let the distance of the place be x km then,
Ex. A boat covers 24 km upstream and 36 km downstream in 6 hours another time it covers 36 km upstream and 24 km downstream in 13 / 2 hours. Find out the rate of current ?
Solution : Let the rate of upstream be x kmph , rate of downstream be y kmph, then
On adding both equation :
On subtracting both equation :
On solving both final equations we get x=8 and y=12, now
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