There's construction going on in my university, and I found some fascinating figures written on one of the walls (presumably by the construction workers). It looked like someone had gone to a lot of trouble to prove that 7*13=28. Actually, assuming you can play mix 'n' match with units and tens, it's quite convincing! But it's driving me nuts. Can someone look at the attatched thumbnail and tell me what's really going on? EDIT: the "figure 1" "figure 2" "figure 3" are my own additions.