Question

the speed of a boat in still water is 15 kilometre per hour and the speed of a stream is 5 kilometre per hour find the time taken by the boat to cover 40 kilometre upstream and 36 kilometre downstream​

Answer 1

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Answer:

Step-by-step explanation:

The speed of the boat in still water is 15km/hr.It can go 30 km upstream and return to down stream in 41/2hrs.find the speed of the stream.

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let x=speed of stream

(15+x)=speed of boat downstream

(15-x)=speed of boat upstream

travel time=distance/speed

30/(15+x)+30/(15-x)=9/2

60/(15+x)+60/(15-x)=9

LCD: (15+x)(15-x)

60(15-x)+60(15+x)=9(15+x)(15-x)

60(15-x+15+x)=9(225-x^2)

60(30)=2025-9x2

9x^2=2025-1800

9x2=225

take sqrt of both sides

3x=15

x=5

speed of stream=5 km/hr

Answer 2

Answer:

heyyy ,here your right ans.....

time=distance /speed

in upstream,speed=speed of boat-speed of stream.

so, 15-5=10

in downstream ,speed=speed of boat +speed of stream.

so,15+5=20

so ,speed in upstream =40/10=4hower............(1)ans.

speed in downstream

=36/20=1.8 howers

=108minuts............(2)ans.