document.write( "Question 734376: if a takes an old sweeper 30 hour to clean a street and takes a new and old sweepers together only 7.5 hours to clean the same street, then how long would it take for new sweeper to cleanse the same street? \n" ); document.write( "
Algebra.Com's Answer #852851 by math_tutor2020(3828)\"\" \"About 
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\n" ); document.write( "There are many great answers by the other tutors.\r
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\n" ); document.write( "\n" ); document.write( "Here's yet another approach.
\n" ); document.write( "Let's say the street length is 3000 feet in total.
\n" ); document.write( "The value 3000 doesn't matter and can be changed to any other number you want, since the final answer at the end will be the same.\r
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\n" ); document.write( "\n" ); document.write( "The old sweeper does the full job in 30 hours when working alone.
\n" ); document.write( "The old sweeper's rate is (3000 ft)/(30 hr) = 100 feet per hour.\r
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\n" ); document.write( "\n" ); document.write( "The new sweeper takes x hours to do the job when working alone.
\n" ); document.write( "The new sweeper's rate is 3000/x feet per hour.\r
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\n" ); document.write( "\n" ); document.write( "Their combined rate is 100 + (3000/x) feet per hour.
\n" ); document.write( "This assumes that neither sweeper hinders the other.
\n" ); document.write( "Multiplying this combined rate by 7.5 hours should lead to the total 3000 feet needed to be cleaned.
\n" ); document.write( "7.5*( 100 + (3000/x) ) = 3000
\n" ); document.write( "which solves to x = 10\r
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\n" ); document.write( "\n" ); document.write( "Therefore the new sweeper needs 10 hours to clean the entire street by itself.
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