Question 123561
{{{n}}} = number of nickels
{{{d}}} = number of dimes
{{{d = n + 3}}}
{{{10d - 20 + 5n = 310}}}
Substitute {{{d}}} in the 1st for {{{d}}} in the 2nd
{{{10(n + 3) - 20 + 5n = 310}}}
{{{10n + 30 - 20 + 5n = 310}}}
{{{15n + 10 = 310}}}
{{{15n = 300}}}
{{{n = 20}}}
He has 20 nickels
check answer
{{{d = n + 3}}}
{{{d = 20 + 3}}}
{{{d = 23}}}
{{{10d - 20 + 5n = 310}}}
{{{10*23 - 20 + 5*20 = 310}}}
{{{230 - 20 + 100 = 310}}}
{{{310 = 310}}}
OK