document.write( "Question 149150: The price of a 2-hour plumbing repair job is $140 and the price of a 5-hour job is $290. Use the slope to predict the cost of a repair job lasting 4 hours. \n" ); document.write( "
Algebra.Com's Answer #109430 by nerdybill(7384)\"\" \"About 
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The price of a 2-hour plumbing repair job is $140 and the price of a 5-hour job is $290. Use the slope to predict the cost of a repair job lasting 4 hours.
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\n" ); document.write( "Think of it this way... The x-axis represents hours. The y-axis is cost of the job.
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\n" ); document.write( "So, now we have two points:
\n" ); document.write( "(2, 140)
\n" ); document.write( "(5, 290)
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\n" ); document.write( "Using \"slope\" formula of two points:
\n" ); document.write( "slope = (290-140)/(5-2) = 150/3
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\n" ); document.write( "Now, using the slope (150/3) and one of the two points (2,140), we can derive the \"slope - intercept\" equation:
\n" ); document.write( "y = mx + b
\n" ); document.write( "plugging in what we know:
\n" ); document.write( "140 = (150/3)(2) + b
\n" ); document.write( "140 = (300/3) + b
\n" ); document.write( "140 = 100 + b
\n" ); document.write( "40 = b
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\n" ); document.write( "Now we have the equation:
\n" ); document.write( "y = (150/3)x + 40
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\n" ); document.write( "To predict the cost for 4 hour job, substitute 4 for x and solve for y:
\n" ); document.write( "y = (150/3)4 + 40
\n" ); document.write( "y = (600/3) + 40
\n" ); document.write( "y = 200 + 40
\n" ); document.write( "y = $240\r
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