document.write( "Question 1151526: It took Millie a total of 4 hours to drive 75 miles to airport and fly 2100 miles to a city in Mexico. If the plane rate is 12 times faster than her car, how fast did she drive? \n" ); document.write( "
Algebra.Com's Answer #773300 by greenestamps(13203)\"\" \"About 
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\n" ); document.write( "12 times faster than the car? or 12 times AS FAST?

\n" ); document.write( "They mean different things, and of course the answers will be different....

\n" ); document.write( "If the car's speed is x, then \"12 times AS FAST AS\" the car is 12x.

\n" ); document.write( "If the car's speed is x, then \"12 times FASTER THAN\" the car is x, plus 12 more times x, or x+12x = 13x.

\n" ); document.write( "Unfortunately, in everyday usage the two phrases are used to mean the same thing.

\n" ); document.write( "Nearly always, when you see the phrase \"x times faster than...\" the intended meaning is \"x times as fast as...\".

\n" ); document.write( "In this problem, \"12 times as fast as\" gives a \"nice\" answer but \"12 times faster than\" does not. So we can assume the intended meaning is \"12 times as fast as\".

\n" ); document.write( "So....

\n" ); document.write( "Let x be the speed of the car; then the speed of the plane is 12x.

\n" ); document.write( "The time to drive 75 miles at x mph is 75/x; the time to fly 2100 miles at 12x mph is 2100/(12x).

\n" ); document.write( "The total time is 4 hours:

\n" ); document.write( "\"75%2Fx+%2B+2100%2F%2812x%29+=+4\"

\n" ); document.write( "Multiply everything by 12x to clear the fractions:

\n" ); document.write( "\"12%2A75+%2B+2100+=+4%2A12x\"
\n" ); document.write( "\"3000+=+48x\"

\n" ); document.write( "You can finish from there....

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