Question 342344
Let D be the number of dimes, P the number of pennies.
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{{{D=2P}}}
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{{{10D+P=231}}}
{{{10(2P)+P=231}}}
{{{20P+P=231}}}
{{{21P=231}}}
{{{highlight(P=11)}}}
Then from the first equation,
{{{D=2(11)}}}
{{{highlight(D=22)}}}