Question 105609
Ans.:    12 D, 8 Q 

Let {{{x }}} be the number of quarters, and {{{y}}} be the number of dimes.
Then:
{{{x+y = 20}}}

Or, we can write:
{{{20 – x }}}as a number of dimes 

We know that sum of quarters and dimes is {{{$3.20=320 pennies}}}, so
We ca write following equation:

{{{25x}}} +{{{10}}}*{{{20-x)}}} = {{{320 }}}

{{{25x +200}}} – {{{10x}}} = {{{320}}}

{{{15x = 320 – 200}}}

{{{15x = 120}}}

{{{x = 120/15}}}

{{{x = 8}}}

{{{x = 8}}}{{{ quarters}}} 

Then, {{{20 – x = 12}}}{{{ dimes}}}