Question

solve this question.

Answer 1

HELLO DEAR,


given that:-


Speed of water = 15km/hr

Distance travelled by upstream and downstream = 30 km


Time= 4hour 30 minutes = 4/2 hours


LET THE SPEED OF STREAM BE X

THEN,

(15+x)=speed of boat in downstream
so, time taken to travel 30km downstream = (30/15+x)

-----------------------AND------------------------

(15-x)=speed of boat in upstream

So, time taken to travel 30km upstream = (30/15-x)




we know that:-

TIME = distance / speed

$\frac{30}{15 + x} + \frac{30}{15 - x} = \frac{9}{2} \\ = > 30( \frac{15 - x + 15 + x}{(15 - x)(15 + x)} ) = \frac{9}{2} \\ = > \frac{30}{225 + 15x - 15x - {x}^{2} } = \frac{9}{2 \times 30} \\ = > \frac{30}{225 - {x}^{2} } = \frac{3}{20} \\ = > \frac{10}{225 - {x}^{2} } = \frac{1}{20} ...........mutiply \: both \: side \: by \: (\frac{1}{3} ) \\ = > 225 - {x}^{2} = 200 \\ = > {x}^{2} = 225 - 200 \\ = > {x}^{2} = 25 \\ = > x = \sqrt{25} \\ = > x = 5$

${So, speed of the stream = 5 km/hr}$
$I \: \: \: HOPE \: \: ITS \: \: HELP \: \: YOU \: \: DEAR, \: THANKS$