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Rule of Three
If it takes four men one day to build a wall, how long does it take 60,000 men to build a similar wall?
Crossing the Atlantic
Every day at noon a boat leaves Le Havre for New York while another boat leaves New York for Le Havre. The ocean crossing takes seven days. How many boats will each boat cross during their journey?
The Lady or the Lions
The King showed the Princess a map of the maze and the Princess was allowed to decide which room she would wait in. She was not allowed to send a copy to her lover who would have to guess which path to follow. Which room should she wait in to give her lover the greatest chance of finding her?
Stage: 3 Challenge Level: 
On a clock the three hands - the second, minute and hour hands - are on the same axis. How often in a 24 hour day will the second hand be parallel to either of the two other hands?
NRICH is part of the family of activities in the Millennium Mathematics Project.