"And do you use the same number for your other cash card?" I asked.
"Certainly not!" he replied. "Though that is also a four-digit perfect square, and I can tell you that it comprises four consecutive digits, though not in the right order, of course." What are the Prof's numbers? (Answer on Monday).
2+1 cross; 1 returns; 10+5 cross; 2 returns; 2+1 cross: Total time: 2+1+10+2+2 = 17 minutes.