Question

A boat goes 24 km upstream and 35 km downstream in
9 hour. It was goes 30 km upstream and 21 km downstream in 8 hour. The speed of the boat in still water is:​

Answer 1

Step-by-step explanation:

boat goes 24 km upstream and 35 km downstream in

9 hour. It was goes 30 km upstream and 21 km downstream in 8 hour. The speed of the boat in still water is:

Answer 2

Step-by-step explanation:

Let the speed of the boat in still water be x kilometer/ hour

The speed of boat in stream water be Y kilometer/ hour

speed downstream = x + y km/hr

speed upstream= x -y km/hr

According to the question-

time for downstream =

distance/ speed=24 / x + y

time for upstream = distance/ speed equal to 35/ x- y

total time = 9 hour

therefore (24 / x + y)+ (35/x - y) = 9

Also= (21/ x+ y)+ (30/ x-y) = 8

let 1/ X + Y = a;. 1/ x - y = b

Therefore,

24a + 35 b= 9. × 6

21a + 30 b = 8. × 7

--------------------

144a + 210b= 54

147a + 210b= 56

-----------------------. signs change as subtraction

-3a. = -2

a= 2/3

substitute for b

24(2/3) + 35 b= 9

16+35b= 9

b= -7/35

b= -1/5

substitute a as 1 / X + Y and b as 1/ x - y

2/3= 1/x+y. and -1/5= 1/x-y

x+y= 3/2. and

x-y= -5

2x= -7/2

x= -7/4

substitute in y

-7/5 -y= -5

-y= -5+7/5

y= 18/5

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