Question

A boat goes 64 km upstream and 72 km downstream in 14 hrs. It goes 80 km upstream and 96 km downstream in 18 he's.find the speed of boat in still water and speed of stream

Answer 1

Let the speed of boat in still water be x and speed of stream be y 

64/ ( x-y) + 72 / (x+y) = 14 

80/ (x-y) + 96 / (x+y) = 18 

Let x-y be = a and x+y be = b 

64/ a + 72/b = 14 

80/a + 96/b =18 

MULTIPLY EQUATION 1 BY 4 AND EQUATION 2 BY 3 

256/a + 288/b = 56 

240/a + 288/b = 54 

SUBTRACT 16/a = 2 

a= 8 

240/8 + 288/b = 54 

288/b = 24 

b = 12 


x+y = 12 

x-y = 8 

ADD 2x = 20 

x =10 km/ hour y = 2 km/ hour ANSWER 

CHECK 

64/ (10-2) + 72 / (10+2) = 8 + 5= 14 hours

Answer 2

let the speed of the boat be- X
let the speed of the strem be-Y
Speed of up stream be x-y
speed of down stream be x+y



1) 64 72
_____ +____ =14
x-y x+y


2) 80 96
________ +_______ = 18
x-y x+y

then quate these two equations