document.write( "Question 175252: Barbara and Ramir raced each other. Barbara averaged 9 mph for the entire course while Ramir averaged 8 mph for the fist half of the course and 10 mph for the second half. Who won? \n" ); document.write( "
Algebra.Com's Answer #130349 by gonzo(654) ![]() You can put this solution on YOUR website! it appears that barbara is the winner. \n" ); document.write( "here's why: \n" ); document.write( "--- \n" ); document.write( "let t = time it took barbara. \n" ); document.write( "since rate * time = distance, then \n" ); document.write( "9*t = d \n" ); document.write( "which means that \n" ); document.write( "t = d/9 \n" ); document.write( "barbara took d/9 hours to cover the distance. \n" ); document.write( "--- \n" ); document.write( "let t1 = time it took ramir to cover half the distance at 8 mph. \n" ); document.write( "since rate * time = distance, then \n" ); document.write( "8*t1 = d/2 \n" ); document.write( "which means that \n" ); document.write( "t1 = d/16 \n" ); document.write( "--- \n" ); document.write( "let t2 = time it took ramir to cover half the distance at 10 mph. \n" ); document.write( "since rate * time = distance, then \n" ); document.write( "10*t2 = d/2 \n" ); document.write( "which means that \n" ); document.write( "t2 = d/20 \n" ); document.write( "--- \n" ); document.write( "the total time it took ramir is equal to t1 + t2. \n" ); document.write( "since t1 = d/16 and t2 = d/20, then \n" ); document.write( "t1 + t2 = d/16 + d/20 \n" ); document.write( "--- \n" ); document.write( "d/16 + d/20 = (20d + 16d) / (16*20) \n" ); document.write( "which equals \n" ); document.write( "36d / 320 \n" ); document.write( "which equals \n" ); document.write( "d/8.888888888..... hours \n" ); document.write( "--- \n" ); document.write( "t1 + t2 = d/8.8888888.... hours which is the time it took ramir. \n" ); document.write( "--- \n" ); document.write( "since d/9 is a smaller number than d/8.8888888....., this means that barbara is the winner. \n" ); document.write( "--- \n" ); document.write( "this answer should be good at any distance. \n" ); document.write( "as an example, let d = 90 \n" ); document.write( "it took barbara 10 hours \n" ); document.write( "it took ramir 10.125 hours. \n" ); document.write( "this is 45/8 + 45/10 since he covered half the distance at 8 mph and half the distance at 10 mph. \n" ); document.write( "--- \n" ); document.write( "let d = 1500 miles \n" ); document.write( "it took barbara 166.7 hours (rounded) \n" ); document.write( "it took ramir 168.75 hours. \n" ); document.write( "this is 750/8 + 750/10 since he covered half the distance at 8 mph and half the distance at 10 mph. \n" ); document.write( "--- \n" ); document.write( "answer checks out ok. \n" ); document.write( "barbara is the winner at any distance. \n" ); document.write( " |