document.write( "Question 1207221: A motorboat travels the distance from one pier to another pier in 4 hours and the way back in 5 hours. What is the speed of the boat in still water if it travels 70 km with the current in 3.5 hours? \n" ); document.write( "

Algebra.Com's Answer #844970 by ikleyn(52814) $\"\"$ $\"About$

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\n" ); document.write( "A motorboat travels the distance from one pier to another pier in 4 hours
\n" ); document.write( "and the way back in 5 hours. What is the speed of the boat in still water
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document.write( "70 km with the current in 3.5 hours means the speed downstream is  70/3.5 = 20 km/h.\r\n" );
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document.write( "The trip in 4 hours  downstream with the speed of 20 km/h means that one way distance is 20*4 = 80 km.\r\n" );
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document.write( "Spending 5 hours upstream the distance 80 km means that upstream speed is 80/5 = 16 km/h.\r\n" );
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document.write( "Having the speeds 20 km/h downstream and 16 km/h upstream means that the average of these two values is\r\n" );
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document.write( "     =  = 18 km/h.\r\n" );
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document.write( "This average is the speed of the boat in still water - so, the speed of the motorboat in still water is 18 km/h.    ANSWER\r\n" );
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