On a recess between my classes one of my students opens a handbook on algebra. He tries to do the calculations he didn't finish (or even didn't start) in class. 1/2 + 1/3. After a minute of whispering and fidgeting on a chair the boy opens an envelope with paper stripes divided into the equal sections (a stripe with 3 sections, a stripe with 5 sections) and puts them one over the other to get the answer in such an exotic way.