A boat covers a distance of 20 kilometres upstream in 15 minutes. It covers the same
distance downstream in 10 minutes. What is the speed of the river?
A. 30 km/hr
B. 50 km/hr
C. 100 km/hr
D. 20 km/hr
Answers
Answer:
20 km/hr.
Step-by-step explanation:
It goes 20 km upstream.
Therefore, distance is 20 km.
Time is given as 15 minutes,which is 1/4 hours for going upstream.
Also, time given for downstream is 10 minutes or 1/6 hrs.
let the speed of boat = x, speed of water current = y.
speed of the boat while going upstream will be x-y km/hr , since the boat is having an opposing speed from water current.
Net speed of boat while going upstream= distance/time.
implies, - x-y = 20km/ 1/4 hours.
x-y = 80.
Speed of the boat while going downstream will be x+y km/hr, since the water current adds on to the speed of the boat.
hence similarly, x+y = 20km/ 1/6 hours.
x+y = 120.
using elimination, we get
x+y = 120
x-y = 80
________
2x =200
x=100.
since x+y = 100,
y = 20 when x is substituted.
hope it helps.
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