The big picture
One card with five holes did four jobs in this track.
| Idea | Remember |
|---|---|
| Numbers on cards | In binary, each place is worth twice the place on its right. Add the places that have a 1. |
| Letters on cards | Four holes give 16 patterns. Five holes give 32. So 26 letters need five holes. |
| Sorting with a needle | Sort by the 1 hole first and the 16 hole last. Put the open-hole pile behind. |
| A lights puzzle | Each clue keeps only the settings that obey it. When one setting is left, that is the answer. |
A hole is a bit. Five bits make 32 patterns. A code gives each pattern a meaning. A pass of the needle uses one bit at a time.
Your school handbook has a punched-card activity and a lights puzzle. You have now done the thinking behind both.