document.write( "Question 1071692: A boat travels 7 km upstream and 7km back. The time for the round trip is 4 hrs. The speed of the stream is 3 ​km/hr. What is the speed of the boat in still​ water? \n" ); document.write( "
Algebra.Com's Answer #686622 by stanbon(75887)\"\" \"About 
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A boat travels 7 km upstream and 7km back. The time for the round trip is 4 hrs. The speed of the stream is 3 ​km/hr. What is the speed of the boat in still​ water?
\n" ); document.write( "Upstream DATA:
\n" ); document.write( "dist = 7 km ; time = t hrs ; rate = 7/t km/hr
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\n" ); document.write( "Downstream DATA:
\n" ); document.write( "dist = 7 km ; time = 4-t hrs ; rate = 7/(4-t) km/hr
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\n" ); document.write( "Rate Equations:
\n" ); document.write( "b - 3 = 7/t
\n" ); document.write( "b + 3 = 7/(4-t)
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\n" ); document.write( "Solve for \"t\"::
\n" ); document.write( "[7/t]+3 = [7/(4-t)]-3
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\n" ); document.write( "7/(4-t) - 7/t = 6
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\n" ); document.write( "[7t-7(4-t)]/(4t-t^2) = 6
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\n" ); document.write( "14t-28 = 24t - 6t^2
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\n" ); document.write( "6t^2 - 10t - 28 = 0
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\n" ); document.write( "3t^2 - 5t -14 = 0
\n" ); document.write( "t = 3.15 hrs
\n" ); document.write( "---
\n" ); document.write( "Solve for \"b\":
\n" ); document.write( "b-3 = 7/t
\n" ); document.write( "b = 7/3.15 + 3
\n" ); document.write( "boat speed = 5.22 km/hr
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\n" ); document.write( "Cheers,
\n" ); document.write( "Stan H.
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