problem
Zeller's birthday
Age
14 to 16
Challenge level
What day of the week were you born on? Do you know? Here's a way to
find out.
problem
Sorted
Age
14 to 18
Challenge level
How can you quickly sort a suit of cards in order from Ace to King?
problem
Flow chart
Age
11 to 14
Challenge level
The flow chart requires two numbers, M and N. Select several values for M and try to establish what the flow chart does.
problem
Substitution cipher
Age
11 to 14
Challenge level
Find the frequency distribution for ordinary English, and use it to help you crack the code.