document.write( "Question 1174166: A biology teacher drives from Naperville over the Cleveland to visit her sister. During the trip there, she travels the first half of the time at 65 km/hr and the second half the time at 95 km/hr. When she comes back, she drives the first half the distance at 65 km/hr and the second half of the distance at 95 km/hr. What is her average speed coming back from Cleveland?\r
\n" ); document.write( "\n" ); document.write( "I am confused how to calculate this. I thought it might just be the average of the two speeds but that is not the correct answer. Also, I tried to set up an equation, but solving this did not give me the right answer. The equation I thought might work (wrong answer of 78.6 km) was D/160 + D(1/260 + 1/380), and then divided 1 by 0.0127 (sum of all the D terms). Any help would be greatly appreciated. Thank you.\r
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Algebra.Com's Answer #799569 by ikleyn(52803)\"\" \"About 
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\n" ); document.write( "A biology teacher drives from Naperville over the Cleveland to visit her sister.
\n" ); document.write( "During the trip there, she travels the first half of the time at 65 km/hr and the second half the time at 95 km/hr.
\n" ); document.write( "When she comes back, she drives the first half the distance at 65 km/hr and the second half of the distance at 95 km/hr.
\n" ); document.write( "What is her average speed coming back from Cleveland?
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document.write( "Let \" t \" be her total time driving from N to C.\r\n" );
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document.write( "Then the total distance from N to C is  d = 0.5t*65 + 0.5t*95 = 0.5t*(65+95) = 0.5t*160 = 80t  kilometers.\r\n" );
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document.write( "Half the distance is 40t kilometers.\r\n" );
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document.write( "When driving back (from C to N),  the total driving time is  T = \"40t%2F65\" + \"40t%2F95\"  hours.       (1)\r\n" );
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document.write( "The average speed driving back is the total distance  80t  divided by the total time of the formula (1), i.e.\r\n" );
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document.write( "    \"V%5Baverage%5D\" = \"80t%2F%28%2840t%29%2F65+%2B+%2840t%29%2F95%29\" = \"2%2F%281%2F65%2B1%2F95%29\" = 77.1875 kilometers per hour.    ANSWER\r\n" );
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\n" ); document.write( "\n" ); document.write( "Is everything clear to you in my solution ?\r
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\n" ); document.write( "\n" ); document.write( "When you complete read it, do not forget to post your \"THANKS\" to me for my teaching.\r
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\n" ); document.write( "\n" ); document.write( "For the problem,  it does not matter,  who is the driver:  \"biology teacher\",  or carpenter,  or sales manager,  or astronaut,
\n" ); document.write( "or vice-president,  or anybody else.\r
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\n" ); document.write( "\n" ); document.write( "Therefore,  naming his  (or her)  specialty is  IRRELEVANT  to the problem.\r
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\n" ); document.write( "\n" ); document.write( "I know that  80%  of problems in  US  Math textbooks are formulated this way.\r
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\n" ); document.write( "\n" ); document.write( "It is  NOT  an argument that they all are correct;  they all are WRONG.\r
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\n" ); document.write( "\n" ); document.write( "They teach young students to think incorrectly,   and,  in addition,  they treat the students inadequately . . . \r
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\n" ); document.write( "\n" ); document.write( "As a result,  when such a student sees the words  \"vice-president\"  instead of  \"biology teacher\",
\n" ); document.write( "he  (or she)  thinks that it is another problem . . . \r
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