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:

D.20 km/hr

Step-by-step explanation:

b= boat speed

r = river speed

during upstream,

speed = b - r

speed = dist/time = 20km/0.25hr = 80km/hr

so b-r = 80 --- 1

during downstream,

speed = b+r

speed = dist/time = 20km/(10/60)hr = 120 km/hr

so b+r=120---- 2

solving both equations we get b and r

1 + 2 =>

2b= 200

b=100km/hr

b-r=80 => r=100-80=20

r =20km/hr