Question

In one hour, a boat goes 11km along the stream and 5 km against it. find the speed of the boat in still water

Answer 1

let the speed of boat be x and speed of stream be y
In one hour, a boat goes 11km along the stream
so speed in upstream is (x-y)=5
In one hour, a boat goes 5km against it
so speed in downstream is (x+y)=11
we have pair of linear equations
1. (x-y)=5
2. (x+y)=11
by substitution method
eqn1. x=5+y
putting x in eqn 2
(x+y)=11
5+y+y=11
2y=6
y=3
putting value of y in eqn 1
(x-y)=5
x-3=5
x=5+3
x=8km/hr
from above speed of boat is 8km/hr