document.write( "Question 885040: Find out the average speed of person who rides the first mile at the rate of 8 miles an hour, the next mile at the rate of 7.5 miles an hour and the third mile at the rate of 5.5 miles an hour. \n" ); document.write( "
Algebra.Com's Answer #534876 by Alan3354(69443)\"\" \"About 
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Find out the average speed of person who rides the first mile at the rate of 8 miles an hour, the next mile at the rate of 7.5 miles an hour and the third mile at the rate of 5.5 miles an hour.
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\n" ); document.write( "total time = 1/8 + 1/7.5 + 1/5.5 hours
\n" ); document.write( "Total distance = 3
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\n" ); document.write( "General solution, using speeds of a, b & c:
\n" ); document.write( "time = 1/a + 1/b + 1/c = (ab + ac + bc)/abc hours
\n" ); document.write( "Distance = 3 miles
\n" ); document.write( "Avg speed = d/t = 3abc/(ab + ac + bc)
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\n" ); document.write( "Sub the numbers:
\n" ); document.write( "Avg = 3*8*7.5*5.5/(8*7.5 + 8*5.5 + 7.5*5.5)
\n" ); document.write( "= 990/(60 + 44 + 165/4) = 990/(581/4)
\n" ); document.write( "= 3960/581 mi/hr
\n" ); document.write( "=~ 6.8158 mi/hr
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\n" ); document.write( "Note: avg = 3abc/(ab + ac + bc) is the same as 3 resistors in parallel, times 3
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