Speed of motorboat in still water is $45 k m / h$ . If the motorboat travels $80 k m$ along the stream in $1 h 20 m i n$ , then the time taken by it to cover the same distance against the stream will be

4 h 20 m i n

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3 h 40 m i n

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2 h 40 m i n

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2 h 55 m i n

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Solution

The correct option is C $2 h 40 m i n$
We have,
$\begin{matrix} 1 h r 20 min = (1 + \frac{1}{3}) h r (1 + \frac{1}{3}) h r = \frac{80}{45 + x} L e t t h e s p e e d o f s t r e a m b e x k m / h r \frac{4}{3} = \frac{80}{45 + x} 45 + x = 60 \Rightarrow x = 15 k m / h t = \frac{8}{45 + x} = \frac{80}{80} = \frac{8}{3} h r = (2 + \frac{2}{3}) h r = 2 h r 40 min \end{matrix}$

Option $C$ is correct answer.

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Speed of motorboat in still water is 45 km/h. If the motorboat travels 80 km along the stream in 1 h20 min, then the time taken by it to cover the same distance against the stream will be

The correct option is C 2 h40 minWe have,1hr20min=(1+13)hr(1+13)hr=8045+xLetthespeedofstreambexkm/hr43=8045+x45+x=60⇒x=15km/ht=845+x=8080=83hr=(2+23)hr=2 hr 40minOption C is correct answer.

Speed of motorboat in still water is $45 k m / h$ . If the motorboat travels $80 k m$ along the stream in $1 h 20 m i n$ , then the time taken by it to cover the same distance against the stream will be