Hello and welcome to Chalk Dust and Common Sense. I am Ciara Mulvaney, I taught maths for nine years, and I now spend my days with adults who were told they could not do it. Today we start with percentages, because they are everywhere and because they cost people real money. Here is the puzzle. A jacket is 100 euro. The shop takes 20 percent off. Then the sale ends and they put 20 percent back on. Is the jacket 100 euro again? Most people say yes. It is not, and once you see why, you will never be fooled by a headline or a discount again. I will give you a few tricks for doing this in your head, and at the end a listener asks about service charges on restaurant bills. No calculator needed, just your ears. You are listening on Witspeak Podcasts.