Question 1049259
1.{{{Q+D=13}}} Total number of coins
.
.
{{{25Q+10D=250}}} Total value of coins
2.{{{5Q+2D=50}}}
Subtract two times eq. 1 from eq. 2,
{{{5Q+2D-2Q-2D=50-2(13)}}}
{{{3Q=24}}}
{{{Q=8}}}
Then from eq. 1,
{{{8+D=13}}}
{{{D=5}}}