The speed at which a boy can row a boat in still water is 60 kmph. If he rows downstream, where the speed of current is 12 kmph, what time will he take to cover 400 metres?  Select.
A) 17  B) 18  C) 19  D) 20  E) 21
Speed of the boat downstream = 60 + 12= 
<gadget id="calculator">60 + 12</gadget>
<output>72</output>
72 kmph= 72 * 5/18= 
<gadget id="calculator">72 * 5/18</gadget>
<output>20</output>
20 m/s   Hence time taken to cover 400 m= 400/20= 
<gadget id="calculator">400/20</gadget>
<output>20</output>
20 seconds.   Answer: 20
<result>D</result>
The speed at which a boy can row a boat in still water is 60 kmph. If he rows downstream, where the speed of current is 12 kmph, what time will he take to cover 400 metres?