Question

A river 2km wide is flowing at the rate of 2km/have. A boatman can row the boat at a speed of 4km/have in still water goes a distance of 2km upstream and then comes back. The time taken by m s journey is a)60 mom b)70 min c)80 min d)90 min

Answer 1

Speed of water is 2 Km/hr, Speed of Boat is 4 Km/hr,Up stream Speed = 4-2 = 2 Km/hr,Down Stream Speed = 2+4 = 6 Km/hr,So Total time = 2/6 + 2/2 =4/3 hr =4/3*60 =80 min.(c) is correct answer.

Answer 2

Dear Student,

◆ Answer -

(c) 80 min

● Explanation -

# Given -

vr = 2 km/h

vb = 4 km/h

# Solution -

Speed of the boat upstream will be -

vu = vb - vr

vu = 4 - 2

vu = 2 km/h

So time taken to go 2 km upstream is -

tu = s / vu

tu = 2 / 2

tu = 1 h

tu = 60 min

Speed of the boat downstream will be -

vd = vb + vr

vd = 4 + 2

vd = 6 km/h

So time taken to go 2 km downstream is -

td = s / vd

td = 2 / 6

td = 1/3 h

td = 20 min

Total time of journey is -

T = tu + td

T = 60 + 20

T = 80 min

Thanks dear...