document.write( "Question 766473: Luke has 21 coins worth $3.90. If he has only dimes and quarters, how many of each does he have? \n" ); document.write( "

Algebra.Com's Answer #466925 by josmiceli(19441) $\"\"$ $\"About$

You can put this solution on YOUR website!
Let $\"+d+\"$ = number of dimes
\n" ); document.write( "Let $\"+q+\"$ = number of quarters
\n" ); document.write( "--------------
\n" ); document.write( "(1) $\"+d+%2B+q+=+21+\"$
\n" ); document.write( "(2) $\"+10d+%2B+25q+=+390+\"$ ( in cents )
\n" ); document.write( "----------------------
\n" ); document.write( "Multiply both sides of (1) by $\"+10+\"$
\n" ); document.write( "and subtract (1) from (2)
\n" ); document.write( "(2) $\"+10d+%2B+25q+=+390+\"$
\n" ); document.write( "(1) $\"+-10d+-+10q+=+-210+\"$
\n" ); document.write( " $\"+15q+=+180+\"$
\n" ); document.write( " $\"+q+=+12+\"$
\n" ); document.write( "and, since
\n" ); document.write( "(1) $\"+d+%2B+q+=+21+\"$
\n" ); document.write( "(1) $\"+d+%2B+12+=+21+\"$
\n" ); document.write( "(1) $\"+d+=+9+\"$
\n" ); document.write( "He has 9 dimes and 12 quarters
\n" ); document.write( "check:
\n" ); document.write( "(2) $\"+10%2A9+%2B+25%2A12+=+390+\"$
\n" ); document.write( "(2) $\"+90+%2B+300+=+390+\"$
\n" ); document.write( "(2) $\"+390+=+390+\"$
\n" ); document.write( "OK \n" ); document.write( "

\n" );