Question

The speed of a boat upstream is 40% less than the speed of the boat downstream. It takes 13.5

hours to go 120 km downstream and 90 km upstream. How much time (in hours) will it take to go

90km downstream and 120 km upstream?​

Answer 1

Answer:

Let the speed in still water = x km/hr. Takes 20 min. to row 12 km upstream ⇒ speed of u/s = 36 km/hr. Also, time taken for u/s is 1/3 more than for d/s.

Answer 2

Step-by-step explanation:

Given:

Speed in still water = 40 km/h

Distance in downstream = 120 km

Time in downstream = 2 hours

Concept:

Distance is same in both the stream, accordingly we calculate the time.

Formula Used:

Speed of boat in still water = (Speed of boat in downstream + Speed of boat in upstream)/2

Calculation:

Speed in still water = 40 km/h

Speed in downstream = 120/2 = 60 km/h

Let x be the speed of stream.

⇒ 40 + x = 60 km/h [∵ Speed in downstream = Speed of boat in still water + Speed of stream

⇒ x = 20 km/h

⇒ Speed of boat in upstream = 20 km/h

⇒ Time in upstream = (120/20) km/h = 6 hours

∴ Time taken to 120 km in upstream is 6 hours.