Question

A Boat goes 64 km upstreamand 72 km downstream in 14 hours. it goes 80 km upstream and 96 km downstream in 18 hours. find the speed of the boat in still water and the speed of the 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