document.write( "Question 190494: can you help me please.the cost of 20 books is $85.00.some of the books cost $8.00 each and the others cost $3.00 each.how many of each type were bought? \n" ); document.write( "

Algebra.Com's Answer #143036 by jonvaliente(64) $\"\"$ $\"About$

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Let x=no of $8-book
\n" ); document.write( ". y=no of $3-book
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\n" ); document.write( "We know that there were 20 books, so:
\n" ); document.write( " $\"x%2By=20\"$ (1)
\n" ); document.write( ".
\n" ); document.write( "Also, we know that the cost of all the books is $85, so:
\n" ); document.write( " $\"8x%2B3y=85\"$ (2)
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\n" ); document.write( "Let's multiply (1) by 3 to get:
\n" ); document.write( " $\"3%2A%28x%2By%29=20%2A3\"$
\n" ); document.write( " $\"3x%2B3y=60\"$
\n" ); document.write( ".
\n" ); document.write( "Let's subtract this new equation from (2) to get:
\n" ); document.write( " $\"8x%2B3y=85\"$
\n" ); document.write( "- $\"3x%2B3y=60\"$
\n" ); document.write( "===============
\n" ); document.write( " $\"5x=25\"$
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\n" ); document.write( "Dividing both sides by 5 we get:
\n" ); document.write( " $\"5x%2F5=25%2F5\"$
\n" ); document.write( " $\"x=5\"$
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\n" ); document.write( "Now we know that there were 5 8-dollar books and 20-5=15 3-dollar books.
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\n" ); document.write( "To check:
\n" ); document.write( "5*8+15*3=?85
\n" ); document.write( "40+45=?85
\n" ); document.write( "85=85 \n" ); document.write( "

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