If it takes four men one day to build a wall, how long does it take
60,000 men to build a similar wall?
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?
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?
Every $10$ minutes, two buses set out, one from each end.
How many buses will one bus meet on its way from one end to the