Question 346013
Let {{{D}}} be the number of dimes, {{{Q}}} the number of quarters.
1.{{{10D+25Q=900}}}
2.{{{Q=2D}}}
Substitute eq. 2 into eq. 1,
{{{10D+25(2D)=900}}}
{{{10D+50D=900}}}
{{{60D=900}}}
{{{highlight(D=15)}}}
Then from eq. 2,
{{{Q=2(15)}}}
{{{highlight(Q=30)}}}