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Kerry asked a bank teller to cash a $390 check using $20 and $50 dollar bills. If the teller gave her a total of 15 bills, how many of each type of bill did she recieve?
\n" ); document.write( "I don't even know where to start on this problem, please help me.
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\n" ); document.write( "Start by writing what is known.
\n" ); document.write( "Call the $20 bills T and the $50 bills F.
\n" ); document.write( "He got 15 bills, so T+F = 15. See that?
\n" ); document.write( "Then, 20T + 50F = 390. See that? Each $20 bill, or T is 20, etc.
\n" ); document.write( "Now there are 2 eqns in 2 unknowns.
\n" ); document.write( "T+F = 15
\n" ); document.write( "20T + 50F = 390
\n" ); document.write( "From the 1st eqn, T = 15-F
\n" ); document.write( "Substitute that into the 2nd eqn.
\n" ); document.write( "20*(15-F)+ 50F = 390
\n" ); document.write( "300 - 20F + 50F = 390
\n" ); document.write( "30F = 90
\n" ); document.write( "F = 3 (he got 3 $50 bills)
\n" ); document.write( "T has to be the other 12, so
\n" ); document.write( "T = 12
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\n" ); document.write( "As a check:
\n" ); document.write( "20*12 + 50*3 does equal 390
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