Question 335269
Let T be the number of $10 bills, and F be the number of $5 bills.
1.{{{T+F=125}}}
2.{{{10T+5F=1000}}}
Multiply eq. 1 by -5 and add the two equations.
{{{-5T-5F+10T+5F=-625+1000}}}
{{{5T=375}}}
{{{highlight(T=75)}}}
Then from eq. 1,
{{{75+F=125}}}
{{{highlight(F=50)}}}
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75 $10 bills and 50 $5 bills.