There's a Sale! What Percent are you Saving?

I was sitting at the airport, one of my favorite places to find math problems. I'm also an accomplished eavesdropped.  An commercial played on TV, touting a huge savings of $10 off every $25 spent.  The woman behind me turned to her friend and asked, "What percent savings is that?"  I thought it would make an interesting question to ask our students, since they might have lots of different ways to show their number sense as they solve it.