A person can row at 9 kmph and still water. He takes 4 1/2 hours to row from A to B and back. What is the distance between A and B if the speed of the stream is 1 kmph?
Choices.
A) 55 km  B) 20 km  C) 77 km  D) 34 km  E) 22 km
Let the distance between A and B be x km.   Total time = x/(9 + 1) + x/(9 - 1) = 4.5   =&gt; x/10 + x/8 = 9/2 =&gt; (4x + 5x)/40 = 9/2 =&gt; x = 20 km.   Answer: 20 km
<result>B</result>
A person can row at 9 kmph and still water. He takes 4 1/2 hours to row from A to B and back. What is the distance between A and B if the speed of the stream is 1 kmph?