The speed of boat and the speed of the stream will be 15.55 km/hr and 4.45 km/hr, respectively.
Speed is the total distance covered by an object within a particular time interval. Speed is measured in the SI unit of m/s (meter per second).
Here, Let the speed of the boat in still water be x km/hr
Let the speed of the stream be y km/hr
The speed of the boat downstream = (x+y) km/hr
The speed of the boat upstream = (x−y) km/hr
Time= Speed × Distance
4 hours to travel 80 km upstream,
i.e., 4 = 80/(x−y)
3 hours to travel 78 km downstream.
i.e., 3 = 78/(x+y)
Let, 1/(x-y) = a and 1/(x+y) = b
Therefore, 4 = 80/a
7 = 78/b
On solving these equations, we get a= 20 and b = 11.1
1/(x-y) = a and 1/(x+y) = b
1/(x-y) = 20 and 1/(x+y) = 11.1
(x-y) = 20 and (x+y) = 11.1
By adding these two we get,
2x = 31.1
x = 15.55
x-y = 20
y = 20- 15.55
y = 4.45
So, the speed of the boat in still water = 15.55 km/hr
The speed of the stream = 4.45 km/hr
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