Question

A boat travels upstream from Point A to Point B in 5 hours. The same boat travelling the same distance in still water takes 50
minutes more than the time taken to travel downstream. Then what is the time taken to travel downstream from Point A to Point
B (Given that it is more than 2 hours)?
✓​

Answer 1

Step-by-step explanation:

GIVEN: Speed of stream = 10 kmh

Let b = the speed of the boat in STILL (current-less) water

So, speed while travelling UPSTREAM = b - 10

And speed while travelling DOWNSTREAM = b + 10

GIVEN: round trip takes the boat 5 hours and the distance between point A and point B is 120 kms

Let's start with a "word equation"

(travel time UPSTREAM) + (travel time DOWNSTREAM) = 5 hours

time = distance/ speed

So we can write: (120/(b - 10)) + (120/(b + 10)) = 5

Multiply both sides by (b - 10) to get: 120 + (120)(b - 10)/(b + 10) = 5(b - 10)

Multiply both sides by (b + 10) to get: 120(b + 10) + (120)(b - 10) = 5(b - 10)(b + 10)

Expands to get: 120b + 1200 + 120b - 1200 = 5b² - 500

Simplify to get: 240b = 5b² - 500

Rearrange to get: 5b² - 240b - 500 = 0

Divide both sides by 5 to get: b² - 48b - 100 = 0

Factor to get (b - 50)(b + 2) = 0

So, EITHER b = 50 OR b = -2

Since the speed cannot be negative, we know that b = 50 kmh

How long did the upstream journey take?

The boat's UPSTREAM speed = b - 10

= 50 - 10

= 40 kmh

time = distance/ speed

So, the boat's travel time upstream = 120/40 = 3 hours

:)

Answer 2

Step-by-step explanation:

Above answer is correct.......Mark that as Branliest