The speed of a boat in still water is 11 km/hr. It can go 12 km upstream and return downstream to its original point in 2 hr 45 min. Find out the speed of the stream.
Answers
Let the speed of the stream = x km/hr
Speed of the boat in still water = 11km/hr
Speed of the boat downstream = (11 + x) Km/hr
Speed of the boat upstream = (11 – x) Km/hr
As the given details we can form an equation and can be calculated as
12 (11-x + 11+x/121-x2) = 11/4
121-x2 = 11/4
x2 = 25
x = 5
The speed of the stream is 5Km/hr
Answer:
Let the speed of stream is x km/h
Then, speed of boat upstream = (15 - x) km/h
speed of boat downstream = (15 + x) km/h
We know,
Time = distance/speed
Now, A/c to question,
30/(15- x) + 30/(15 + x) = 4hrs 30 min = (4 + 1/2) hrs
⇒ 30[ 1/(15 - x) + 1/(15 + x) ] = 9/2
⇒30[ (15 + x ) + (15 - x)]/(15 - x)(15+ x) = 9/2
⇒30 × 30/(225 - x²) = 9/2
⇒900/(225 - x²) = 9/2
⇒100/(225 - x²) = 1/2
⇒200 = 225 - x²
⇒x = ±5
But x ≠ -5 because speed can't be negative.
so, speed of stream = 5 km/h