A man can row 7 ½kmph in still water. If in a river running at 1.5 km an hour, it takes him 50 minutes to row to a place and back, how far off is the place?
Choose the correct choice from the following choices.
A) 3 km B) 4 km C) 5 km D) 6 km E) None
Sol.   Speed downstream = (7.5 + 1.5)= 
<gadget id="calculator">(7.5 + 1.5)</gadget>
<output>9</output>
9 kmph;   Speed upstream= (7.5 - 1.5)= 
<gadget id="calculator">(7.5 - 1.5)</gadget>
<output>6</output>
6 kmph.   Let the required distance be x km. Then,   x/9 + x/6= 50/60 ⇔ 2x + 3x = [5/6 * 18] ⇔ 5x 2  + 3= 
<gadget id="calculator">2  + 3</gadget>
<output>5</output>
[5/6 * 18] ⇔ 5x= 15 ⇔ x =3.   Hence, the required distance is 3 km.   3 kmnswer 3 km
<result>A</result>
A man can row 7 ½kmph in still water. If in a river running at 1.5 km an hour, it takes him 50 minutes to row to a place and back, how far off is the place?