document.write( "Question 1185996: The length of a rectangle is 5 cm more than 3 times its width. The area of the rectangle is 1428 square cm. Find the length and width of the rectangle.\r
\n" );
document.write( "\n" );
document.write( " \n" );
document.write( "
Algebra.Com's Answer #816866 by greenestamps(13200)![]() ![]() You can put this solution on YOUR website! \n" ); document.write( "The responses from the other two tutors both use formal algebraic methods to solve the problem, which is probably what the student was supposed to do. \n" ); document.write( "However, solving the problem with formal algebra requires solving a quadratic equation using either difficult factoring or the quadratic formula. \n" ); document.write( "So, if formal algebra is not required, the problem is solved much more quickly with a bit of estimation and mental arithmetic. \n" ); document.write( "Note also that, even if a formal algebraic solution is required for the assignment, solving the problem with logical reasoning and mental arithmetic gives you valuable brain exercise. \n" ); document.write( "It might go something like this. \n" ); document.write( "For a very rough estimate, since the length is \"a bit more than 3 times the width\", let the width be x and the length be \"a bit more than 3x\", so that the area (length times width) is 1482. \n" ); document.write( "1482 is a bit more than 3x^2 \n" ); document.write( "1482/3 = 496 is a bit more than x^2 \n" ); document.write( "The square root of 496 is a bit more than 22; so the width should be either 22 or perhaps 21. \n" ); document.write( "Then mental arithmetic determines that 21 is a factor of 1428 while 22 is not, so the width is probably 21. \n" ); document.write( "Dividing 1428 by 21 gives 68; and 68 is 5 more than 3 times 21. So we have the answer. \n" ); document.write( "ANSWERS: width 21, length 68 \n" ); document.write( " \n" ); document.write( " |