Question 44768
Just get your equation {{{x+y=180}}}, rearrang to give y in terms of x:
{{{y=180-x}}}
Now substituite this into the other equation you started with:
{{{$0.05x+$0.1y=$13}}}
{{{$0.05x+$0.1(180-x)=$13}}}
{{{0.05x+18-0.1x=13}}}
{{{-0.05x+18=13}}}
{{{0.05x=5}}}
{{{0.01x=1}}}
{{{x=1/0.01}}}
{{{x=100}}}
Now substitute this value of x into your equation for y:
{{{y=180-x}}}
{{{y=180-100=80}}}
So the pot contains 100 nickels and 80 dimes.

I hope this helps.
P.S. I am trying to start up my own homework help website. I would be extremely grateful if you would e-mail me some feedback on the help you received to adam.chapman@student.manchester.ac.uk
Adam