Answer
No, this is not possible. The friend is wrong.
Work Step by Step
$.25q + .1d = \$2.8$
To test your friend's claim, set the equation like this:
$0.1d+0.25(d+8)=2.8$
$0.1d+0.25d+(.25\times8)=2.8$
$0.35d+2=2.8$
$0.35d=.8$
$d=\frac{.8}{.35}$ or $\frac{16}{7}$
For there to be 8 more quarters, you'd have to have $\frac{16}{7}$ dimes, but that is not possible. So your friend is wrong. Don't let him or her forget it.
