Question 754306
{{{0.05x+0.10y=0.65 }}}
{{{5x+10y=65}}}
{{{highlight(x+2y=13)}}}
{{{2y=-x+13}}}
{{{highlight(y=-(1/2)x+13)}}}


Even so, you know that you cannot split a dime into two nickels but you can use two nickels if you are willing to also use one more or one less nickel.  You can not make 65 cents using even number of nickels, because as said, you cannot split the dime.  


The domain is for the number of nickels, x.  
Take the standard form equation {{{x+2y=13}}}.
{{{x=0}}}, {{{y=13}}}, but you cannot have this.  {{{x>0}}}.  In fact, the smallest x is 1.
{{{y=0}}}, then {{{x=13}}}, and in fact {{{x<=13}}} and only in the whole numbers.


So you have this as rules for the domain:
(*) only odd whole numbers
(*) at least 1, and at most 13.
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DOMAIN FOR x IS { 1, 3, 5, 7, 9, 11, 13 }.
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