Question 1049271
I'll express everything in cents
The value of 20 quarters is:
{{{ 25*20 }}} cents
The value of {{{ d }}} sodas is:
{{{ 75d }}} cents
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The value in cents that Amy has left
after buying {{{ d }}} sodas is:
{{{ 25*20 - 75d }}}
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The number of quarters she has left is:
{{{ ( 25*20 -75d ) / 25 }}}
{{{ ( 500 - 75d ) / 25 }}}
{{{ 20 - 3d }}} answer
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check:
suppose {{{ d = 5 }}}
Amy has left:
{{{ 20 - 3*5 = 5 }}} quarters
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5 sodas cost:
{{{ 5*75 = 375 }}} cents
Amy had {{{ 500 }}} cents, so 
she has left:
{{{ ( 500 - 375 ) / 25 = 125/25 }}}
{{{ 125/25 = 5 }}} quarters left
OK