Question 986683
Let {{{ a }}} = the number of $50 bills you have
Let {{{ b }}} = the number of $100 bills you have
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(1) {{{ a + b = 73 }}}
(2) {{{ 50a + 100b = 5000 }}}
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Multiply both sides of (1) by {{{ 50 }}}
and subtract (1) from (2)
(2) {{{ 50a + 100b = 5000 }}}
(1) {{{ -50a - 50b = -3650 }}} 
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{{{ 50b = 1350 }}}
{{{ b = 27 }}}
and
(1) {{{ a + b = 73 }}}
(1) {{{ a = 73 - 27 }}}
(1) {{{ a = 46 }}}
There are 46 $50 bills and 73 $100 bills
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check:
(2) {{{ 50a + 100b = 5000 }}}
(2) {{{ 2300 + 2700 = 5000 }}}
(2) {{{ 5000 = 5000 }}}
OK