A Calculated Answer
As we left the people mover, we saw a large sign with large numbers.
Almost immediately, slowly at first, Ozzie started calculating using the calculator with no batteries. He found that as you entered the digits, the pattern on the keyboard spelled out letters. The letters spelled out "FIVE". This was the last puzzle and we turned in our answers. We were confident of two answers, and knew we were guessing on the rest. We took almost exactly the whole allowed hour.