Question

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​

Answer 1

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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