Question

A boat takes 150 min less to travel 40 km downstream than to travel the same distance upstream. The speed of the stream is 4 km/hr. What is the downstream speed?

Answer 1

Answer:

16 km/hr

Step-by-step explanation:

Let say boat speed = x km/hr

Stream speed = 4 km/jr

upstream speed = x-4 km/hr

downstream speed = x+4 km/hr

Distance one side = 40 km

Upstream time = 40 / (x-4)  hr

Downstram time = 40/(x+4)  hr

150 min = 5/2 hr

40/(x-4)  - 40/(x+4)  = 5/2

80 (x+4 - x +4)  = 5(x+4)(x-4)

16*8 = x^2 - 16

x^2 = 144

x = 12 km/hr

Downstream speed = 12+4 = 16km/Hr