Answer:
speed of boat is 35 mph
speed of river is 5mph.
Step-by-step explanation:
Let the speed of boat be u mph
let the speed of river be v mph
When boat travel downstream
in that case flow of river will support the speed of boat hence
speed of river will be added to speed of boat
Thus,
speed of boat in downstream = speed of boat + speed of river = u + v
Given
the boat travels at 40 mph downstream
thus,
u + v = 40 -----1
When boat travel upstream
in that case flow of river will oppose the speed of boat hence
speed of river will be subtracted from speed of boat
Thus,
speed of boat in downstream = speed of boat -speed of river = u - v
Given
the boat travels at 30 mph upstream
thus,
u - v = 30 ----2
adding 1 + 2
we have
u + v = 40
+ u - v = 30
2u = 70
u = 70/2 = 35
Thus,
speed of boat is 35 mph
using u = 35 in u + v = 40
we have
35 + v = 40
v = 40 - 35 = 5
Thus, speed of river is 5mph.
