<PRE><B>Question 195539</B>
sol:
speed of the boat in still water= x km/h
speed of the current= y km/h
down stream speed=(x+y) km/h
up stream speed=(x-y) km/h
time=distance/speed
according to the problem 
total distance=18 km
speed of the boat in down stream=(x+y) km/h
time taken  down stream=2hours

distance/speed of down stream= 2h
18/(x+y)=2
multiplying by (x+y) on both sides
18
------   *(x+y)=2*(x+y)
(x+y)
18=2(x+y)
time taken up stream=3hours
distance/speed of upstream=3h
18/(x-y)=3
multiplying by (x-y) on both sides
18
------ *(x-y)=3*(x-y)
(x-y)
18=3(x-y)
2(x+y)=18
dividing by 2 on both sides
2(x+y)/2=18/2
x+y=9 -----(1) equation
3(x-y)=18
dividing by 3 on both sides
3(x-y)/3=18/3
x-y=6 ----(2) equation
solving 1 and 2 equations
x+y=9
x-y=6
------
2x=15
dividing by 2 on both sides
2x/2=15/2
x=7.5
substitute in 1 st equation
x+y=9
7.5+y=9
subtracting 7.5 on both sides
7.5+y-7.5=9-7.5
y=9-7.5
y=1.5
speed of the boat in still water=7.5 km/h
speed of current=1.5 km/h





































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