Q. A boat goes 12 km downstream and comes back to the starting point in 3 hours. If the speed of the current is 3 km/ hr, then the speed (in km/ hr) of the boat in still water is ?
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Let the speed of boat is x km/h.
&time taken = t
In downstream
Speed = (x + 3) km/h
12 km = (x+3)/t ..... 1
In upstream
Speed =( x-3) km/h
12 km = (x_3)/t ......2
Adding 1 & 2
X+3/t + x-3/t = 3
.
.
.
X = 3/2 t .... 3
Putting 3 in 1
12 = (x +3)/t
t = 3/7hr ....... 4
Putting 4 in 1
12 = (x+3)/t
X = 15/7
X = 2.14
&time taken = t
In downstream
Speed = (x + 3) km/h
12 km = (x+3)/t ..... 1
In upstream
Speed =( x-3) km/h
12 km = (x_3)/t ......2
Adding 1 & 2
X+3/t + x-3/t = 3
.
.
.
X = 3/2 t .... 3
Putting 3 in 1
12 = (x +3)/t
t = 3/7hr ....... 4
Putting 4 in 1
12 = (x+3)/t
X = 15/7
X = 2.14
Rajnishkd:
hope answer is correct
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speed of boat = 9 km/hr
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