If a boat goes 7 km upstream in 42 minutes and the speed of the stream is 3 kmph, then the speed of the boat… · ABC26GN3814
Subject: General Aptitude · Chapter: Boats and Streams · Exam: Bank Rec. 2010
If a boat goes 7 km upstream in 42 minutes and the speed of the stream is 3 kmph, then the speed of the boat in still water is :
(a)4.2 km/hr
(b)9 km/hr
(c)13 km/hr
(d)21 km/hr
Answer
Explanation
Rate upstream $=\left(\frac{7}{42} \times 60\right) \mathrm{kmph}=10 \mathrm{kmph}$. Speed of stream $=3 \mathrm{kmph}$. Let speed in still water be $x \mathrm{km} / \mathrm{hr}$. Then, speed upstream $=(x-3) \mathrm{km} / \mathrm{hr}$. $$\therefore x-3=10 \text { or } x=13 \mathrm{km} / \mathrm{hr} .$$
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