1.

A motorboat whose speed is 9 km/hr in still water, goes 15 km downstream and comes back in a total time of 3 hours 45 minutes. Find the speed of the stream.

Answer» Correct Answer - 3 km/hr
Let the speed of the stream be x km/hr.
Then, speed downstream `=(9+x)km//hr`
and speed upstream `=(9-x)km//hr.`
`:." "(15)/(9+x)+(15)/(9-x)=(1)/(4)implies4[(9-x)+(9+x)]=(9+x)(9-x)`
`implies81-x^(2)=72impliesx^(2)=9impliesx=3.`


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