document.write( "Question 615108: A motorboat can go 8 miles downstream on a river in 20 minutes. It takes 30 minutes to go upstream the same 8 miles. Find the speed of the current. \n" ); document.write( "
Algebra.Com's Answer #386970 by ankor@dixie-net.com(22740)\"\" \"About 
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A motorboat can go 8 miles downstream on a river in 20 minutes. It takes 30 minutes to go upstream the same 8 miles. Find the speed of the current.
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\n" ); document.write( "Let s = speed of the boat in still water
\n" ); document.write( "Let c = speed of the current
\n" ); document.write( "then
\n" ); document.write( "(s-c) = effective speed upstream
\n" ); document.write( "and
\n" ); document.write( "(s+c) = effective speed downstream
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\n" ); document.write( "since we will wanting mph, change 20 min to 1/3 hr, and 30 min to 1/2 hr
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\n" ); document.write( "Write a distance equation for each way; (dist = time * speed)
\n" ); document.write( "\"1%2F3\"(s + c) = 8
\n" ); document.write( "\"1%2F2\"(s - c) = 8
\n" ); document.write( "multiply the 1st equation by 3, the 2nd equation by 2:
\n" ); document.write( "s + c = 24
\n" ); document.write( "s - c = 16
\n" ); document.write( "---------- adding eliminates c, find s
\n" ); document.write( "2s = 40
\n" ); document.write( "s = 20 mph boat speed in still water
\n" ); document.write( "then
\n" ); document.write( "20 + c = 24
\n" ); document.write( "c = 24 - 20
\n" ); document.write( "c = 4 mph is the speed of the current
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\n" ); document.write( "You can confirm this with the distance equation each way
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