Question : A boat covers 35 km downstream in 2 h and covers the same distance upstream in 7 h. Find the speed (in km/h) of the boat in still water.
Option 1: 11.25
Option 2: 28.75
Option 3: 18.25
Option 4: 10.55
Correct Answer: 11.25
Solution :
A boat covers 35 km downstream in 2 h and covers the same distance upstream in 7 h.
Let the speed of the boat in still water be $x\ \text{km/h}$.
Let the speed of the stream be $y\ \text{km/h}$.
According to the question,
Speed of boat in downstream = $x+y=\frac{35}{2}$ = 17.5
Speed of boat in upstream = $x-y=\frac{35}{7}$ = 5
Adding the two equations,
$2x= 17.5 + 5$
⇒ $x=11.25$
Hence, the correct answer is 11.25.
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