Question

Two boats on opposite banks of a river start moving towards each other. They first pass each other 1400 meters from one bank. They each continue to the opposite bank, immediately turn around and start back to the other bank. When they pass each other a second time, they are 600 meters from the other bank. We assume that each boat travels at a constant speed all along the journey. Find the width of the river?

Answer 1

S1 = speed of boat 1

t1 = time to do 1400 meters (boat 1)

S1*t1 = 1400

S2 = speed of boat 2

1400 + S2*t1 = X

t2 = time to do X + 600 (boat 2)

S1*t2 = X + 600

S2*t2 = 2X - 600

S1 = 1400/t1

S2 = (X-1400)/t1

T = t2/t1

1400*T = X + 600

X*T - 1400*T = 2X - 600

X = 3600 meters

River is 3600 meters wide